Raman spectroscopy in biology: principles and applications

G)-c -..

FIGURE 1.1. Two components of light (electromagnetic wave). The vectors of the electric and magnetic components are perpendicular to each other and to the direction of light propagation.

direction of propagation (Figure 1.1). When the electric field of this wave interacts with matter, light can be scattered or absorbed. 1.1.

ABSORPTION SPECTROSCOPY

When incident light interacts with a compound, some light may be absorbed. Spectroscopy utilizing this property is called absorption spectroscopy. Readers are probably familiar with ultraviolet (UV) absorption spectroscopy, visible absorption spectroscopy, and infrared (IR) absorption spectroscopy, as these techniques are commonly used in modern biological laboratories. These are indeed part of absorption spectroscopy. There are many different kinds of electromagnetic waves, such as y rays, X rays, UV light, visible light (white light), IR light, microwaves, and radiowaves. The difference lies in their wavelength >.. One can also say the difference is due to the frequency P. Both expressions are correct because wavelength and frequency are inversely proportional:

c

}; =

P

(1.1)

where C is the velocity of the electromagnetic wave. Ultraviolet light has a shorter wavelength than IR light; UV light has a higher frequency then IR. In spectroscopy the term wave number ii is frequently used. The wave number is defined as the number of waves contained in a I-em length and can be expressed as ii = 1/>.. Wave number, wavelength, and frequency have the following relationship: I P ii=X= C

Different types of electromagnetic waves are diagrammed in Figure 1.2.

(1.2)

5

Absorption and Scattering of Light Wavelength in em

JOO

Hl

10

5

10

8

Radio waves

FIGURE 1.2. Different types of electromagnetic waves and their wavelengths. Note that visible light is only a small portion of the overall electromagnetic spectrum.

All electromagnetic waves contain inherent energy, which is expressed by Planck's famous equation:

(1.3)

E = hv

where h is Planck's constant. Since UV light has a higher frequency (or shorter wavelength) than IR light, the former contains more energy than the latter. Ultraviolet and visible absorption spectroscopies involve electronic transitions of a molecule. In other words, a molecule receives the energy of the incident light (UV or visible light) and is excited to a higher electronic level (Figure 1.3). Infrared light has low energy. In IR absorption a molecule absorbs the incident light (lR light) and is excited to a higher vibrational or rotational quantum level, but not to a higher electronic quantum level (Figure 1.4). Frequently IR absorption is expressed by percentage transmission T (the ratio of the intensities of the transmitted I and incident light 10 ) or as absorbance A, which is defined as A = 10g(Io/1).

Higher Electronic {. Level .

CD

o c: .c (; U> .c

vvv--

"

«

f-- -

Electronic Ground Level (Lower Electronic Level)

Wavelength ( Ultraviolet. Visible Region)

FIGURE 1.3. The diagram at the left shows the absorption of light by a molecule, raising it to a higher energy level. This results in the absorbtion spectrum diagramed at the right.

6

Basic Concept and Elementary Theory

J1

Higher Electronic Level

Wavelength (A) (Infrared Light Region)

J

/\ /\ ~--------~:~l V

V-

t

V=O

100,"",

>

.:;l5 Lower

Electronic Level

°1

.=

;f. O,~I

------

A

FIGURE 1.4. The IR absorption spectrum is due to the elevation of vibrational energy of a molecule (left). It does not involve electronic energy transition. IR absorption is customarily expressed either by absorption (upper right) or by transmission (lower right).

1.2.

SCATTERING

Scattering refers to light deflected from the direction of incident-light propagation. The interaction of the electric vector of an electromagnetic wave with the electrons of a compound results in the scattering of the incident light. Such interactions induce periodic vibrations in the electrons of a compound, thereby producing oscillating electric moments. Such oscillating electrons become new sources for emitting radiation, that is, the scattered light. There are three basic types of scattering: 1.

Elastic. Same frequency (wavelength) as the incident light-Rayleigh scattering. 2. Inelastic. Lower frequency (longer wavelength) than that of incident light-Stokes Raman scattering. 3. Inelastic. Higher frequency (shorter wavelength) than that of incident light-anti-Stokes Raman scattering.

In other words, there are two types of Raman scattering. In one type the scattered light has lower energy than the incident light, hence it has lower frequency, and the effect is called Stokes Raman scattering. In the other, the scattered light has higher energy than the incident light, hence it has higher frequency than that of the incident light (anti-Stokes effect of Raman scattering). Rayleigh scattering (same frequency) does not involve a change in the energy content of the incident and scattered lights (Figure 1.5). Rayleigh scattering is most familiar to us. We are able to see objects as a result of light scattering. Experiments show that scattering efficiency is in-

Raman Scattering

,/"~

Incidenl Light

,, ",

"

7

A""-S"'" R,m'" S",,,,,".

R"",." S""",",

A Scattering Cenler J ' ~ -llV

Slokes Raman Scattering

FIGURE 1.5. Diagrammatic presentation of the three types of light scattering: anti-Stokes Raman scattering, Rayleigh scattering and Stokes Raman scattering.

versely proportional to the fourth power of wavelength. Sunlight includes light of many wavelengths. But because blue light has a shorter wavelength than red light, it is scattered more than red light. When we see the blue sky, we are seeing the scattered-primarily blue-portion of sunlight. At sunset and sunrise, sunlight passes through a greater thickness of atmosphere than when the sun shines from above. Since most of the blue short wavelength light has been scattered by molecules in the air, most of the remaining red to orange light passes through. This is the reason why sunset and sunrise appear red to our eyes. Compared with Rayleigh scattering, Raman scattering is less common in our daily lives; nevertheless, it is important for scientists who are interested in vibrational and rotational states of molecules. The Raman process involves two photons with different energies, as the incident photon and scattered photon differ in energy. This energy difference is due to a change in the vibrational or rotational state of a molecule caused by interaction with incident photons. For this reason, analysis of the Raman spectra provide information about molecular properties such as the manner and type of vibrations. The intensity of scattered light is influenced by many factors: 1. The size of the particle or molecule illuminated. 2. The location of observation. The scattering intensity is a function of the angle with respect to the incident beam. 3. The frequency of the incident light. 4. The intensity of the incident light.

2. RAMAN SCATTERING The Raman scattering effect arises from the interaction of the incident light with the electrons in the illuminated molecule. In nonresonance Raman scattering, the energy of the incident light is not sufficient to excite the molecule to a higher electronic level. Instead, Raman scattering results in changing the molecule from its initial vibrational state to a different vibrational state (Figure 1.6).

8

Basic Concept and Elementary Theory Electronic - - - - - - - - - - - - - - - - - ] Excited State -- --- --

-/""""0 at 0=0

Active

o

o

+a +a

oP) (SQ

=

0

at Q=O

No

FIGURE 1.16. Diagram showing the stretching vibration of a diatomic molecule consisting of identical atoms.

.....

Vibrational Modes of Simple Molecules Vibrational Mode

23

@--@

@-----@

Polarizability Ellipsoid

Polarizability Variation With Normal Coordinates

Polarizability Derivative

(~)at Q~O

+0 +0 Active

Raman Activity

Dipole Moment

+,

Dipole Moment Variation With Normal Coordinates

Dipole Moment Derivative

(~~)at Q~O I R Activity

oa) ~o (oQ at Q~O

>

+ I

+0 +0

>

*0 oP\ ( oQl Q~O at

Active

FIGURE 1.17. Stretching vibration of a heterogeneous diatomic molecule. With Hel, such a vibration appears at 2885.9 cm- I in the gas phase, 2785.0 cm- I in the liquid phase, and 2768.0 cm - I in the solid phase.

For the bending vibration, there is no change in polarizability; therefore, it is Raman inactive. But it is IR active (Figure 1.20). In the CO2 , molecule, there is no overlap in fundamental vibrational frequencies between Raman and IR spectra. This is because the CO2 molecule possesses a center of symmetry. This is called the principle of mutual exclusion. There are many other compounds possessing a center of symmetry such as benzene, pyrole, pyrazine, and ethylene (Figure 1.21). The CO2 molecule consists of three atoms. The number of normal vibrations for a linear triatomic molecule should be 3 X 3 - 5 = 4. But actually only

24

Basic Concept and Elementary Theory Vibrational Mode

o-c-o

o-c-o

~

¢:

PoIarizability Ellipsoid

Polarizability

+ +0

Variation

With Normal Coordinates

Polarizability Derivative

(~QL

Q-O

Dipole Moment Variation With Normal Coordinates

Dipole Moment Derivative

(~L

0-0

IR Activity

Sa' ;0/0 SOlat 0 0 0

Active

Raman Activity

Dipole Moment

(

0

0

+0 +-0

(~6)

=0 at 0 0 0

No

FIGURE 1.18. Symmetrical-stretching vibration of a linear triatomic molecule such as CO 2 . It appears at 1285 cm- I in the Raman spectrum but is absent from the IR spectrum because there is no change in dipole moment.

three fundamental vibrational modes appear in Raman and IR spectra. This is due to the degenerate bending of CO2 , One bending takes place in the plane (Figure 1.22A) and the other out of plane (Figure 1.22B). Such "in-plane vibration" and "out-of-plane vibration" have the same energy, hence show the same frequency and are degenerate. So far we have discussed fundamental vibrations only. Actually CO2 produces more than four bands due to other mechanisms such as overtones and

....

Vibrational Modes of Simple Molecules Vibrational Mode

o-c-o

¢=

25

o-c-o

::;>¢=

Polarizability Ellipsoid

Polarizability Variation With Normol Coordinates

Polorizability Derivative

(~~L

0=0

Raman Activity

Dipole Moment

- ++ - (p=o) ¢:=-===:>

With Normal Coordinates

Dipole Moment Derivative 0=0

IR Activity

sa) (SO

=0 ot 0=0

No

Dipole Moment Variation

(~6t

-+a -f-a -

+ ====> + - (P ~ 0

¢:=. -

I

+a

fa

~o (M:.\ S °lat 0=0

Active

FIGURE 1.19. Asymmetrical-stretching vibration of a linear triatomic molecule such as CO 2 , The asymmetrical-stretching vibration of CO 2 is IR active (2349 cm -I) but Raman inactive because there is no change in polarizability, but there is a change in the dipole moment.

Fermi resonance (see Chapter 3, section 1.1). Usually fundamental vibration bands have a higher intensity than other bands. 7.3.

NONLINEAR TRIATOMIC MOLECULES

For nonlinear molecules the total degrees of freedom for vibrations is 3N - 6. Three coordinates are required to specify the position of each atom; thus 3N coordinates are needed for N atoms. Of all these degrees of freedom, three are



o/c" 0

o-c-o

Vibrational Mode

\1

{J Polarizability Ellipsoid

Polarizability Variation With Normal Coordinates

Polarizability Derivative

(~~at

0:0

-+0 fo

Ramon Activity

=0 (ba) bQ at 0:0

No

c 0 / "0

(p=o)

O-C-O

Dipole Moment

Dipole Moment Variation With Normal Coordinates

Dipole Moment Derivative

(~:t I R Activity

0=0

~+

~_

0" /O~C ~+

-+0 +0

(~at 0=0~O

Active

FIGURE 1.20. Bending vibration of a linear triatomic molecule such as CO 2 , This is IR active (667 cm -I for CO 2 ) but Raman inactive.

...

Vibrational Modes of Simple Molecules

o

00

II

C II

o CO 2

Benzene

27

,C=C H ,

H

/

/

H

H

Ethyl ene

Pyrazi ne

FIGURE 1.21. Examples of molecules with a center of symmetry. The symmetry of a molecule has an important relation to IR and Raman activities.

rotational motions and three are translational motions; thus the degrees of freedom remaining for vibrations are 3N - 6. Sulfur dioxide, S02' will be used as an example. The molecule is nonlinear; therefore, a possible maximum number of fundamental vibrations can be calculated from the equation 3N - 6. Accordingly, S02 should have 3 X 3 - 6 = 3 vibrational modes, which are symmetrical-stretching ("I' 1151 cm -I), asymmetrical-stretching ("3' 1361 cm -\), and bending vibrations ("2' 519 cm- 1). Usually the assignment is made for the highest frequency symmetric vibration as "\' and the next highest "2. After all symmetrical vibrations are assigned, then the asymmetric vibrations are counted starting at the highest frequency. In the symmetrical-stretching vibration there are changes in the electron-cloud size (polarizability) and dipole moment; hence this vibration is active in both Raman and IR spectra (Figure 1.23). For the asymmetrical-stretching vibration there is no change in the shape of the polarizability ellipsoid, but the orientation changes as it rocks. Such a vibration is Raman active. This vibration is also IR active, because there is a change in the dipole moment (Figure 1.24). For the bending vibration, both the ellipsoid and dipole moments change; therefore, it is both Raman and IR active (Figure 1.25). The vibrational bands described here are due to fundamental vibrations. Actually S02 shows more than three bands due to overtones (see Chapter 3, section 1.1) and combinations. 7.4.

VIBRATIONAL MODES OF THE METHYLENE GROUP

The C- H in the methylene group has complex vibrations, especially for bending (deformation) vibrations. For stretching vibrations, there are symmetrical and asymmetrical types (Figure 1.26). _o~

·A

P:':'o

,/

I

,/

C

\

o~o

B

[p

O-C

ft /1

d

FIGURE 1.22. Two types of bending vibrations of the CO 2 molecule producing degenerate bending. (A) Bending in the plane. (B) Bending out of plane.

s

{}

CO/s"cf

Vibrational Mode

0/""0

Polarizability Ellipsoid

+a

Polarizability Variation With Normal Coordinates

fa

Palarizability Derivative

(~t

0=0

Ramon Activity

Dipole Moment

n+

\1- 0

/5"

With Normal Coordinates

Dipole Moment Derivative

IR Activity

#0

SQ 010=0

Active

Dipole Moment Variation

(~l 0'

(k)

0=0

0

n+

~-o

/5~

a

+a fa

(~t O=~O

Active

FIGURE 1.23. Symmetrical-stretching vibration of a nonlinear triatomic molecule using S02 as an example (1151 em-I).

"a

lit...

s

S VI brat iona I Mode

0/ '0

0/ "0

Polarizability Ellipsoid

+0 fo

Polarizability Variation With Normal Coordinates

Polarizability Derivative

(~dt

0'0

Roman Activity

Dipole Moment

n:

Dipole Moment Derivative

FIGURE 1.24.

Activity

0=0

n+ s JJ_O/ "0

s 0/ "0

With Normal Coordinates

IR

f'!O SO at 0=0

Active

Dipole Moment Variation

(~~L

(so)

-f-

0

~o

(SP) SO at

¢O 0=0

Active

Asymmetrical-stretching vibration of a nonlinear triatomic molecule using S02 as

an example (1361 em-I).

~Q

Vibrational Mode

{] __.-4'~

!!-=: - -. _ -]II._~.-

~=/~~ DOUBLE

MONOCHROMATOR

)--(])_.y I

"'''' I DJ"'""",," """~~ II'\'

""" .

"'~~""~ ~ N'JJ\g;\ '. I R=D~R' "1 ELECTRONIC

•

... .

,

," ,,

"

.

~ITill"" QJ .. 1~ .. ~ ~~~ ~-

I

A

.

"

','

1\ COMPUTER

FIGURE 2.5. examined.

Essential parts of a Raman spectrometer. Normally the scattered light at 90° is

instrument is often designed to collect scattered light at 90 0 with respect to the incident light. The collected scattered light is aligned and focused to the slit of a double monochromator. In a sophisticated Raman spectrometer, usually two to three monochromators are used. As the ratio of incident light to Ramanscattered light sometimes exceeds 10 9 , high spectral purity is needed to unveil weak Raman spectra. In a double monochromator, light is dispersed in the first monochromator, and it is again dispersed in the second. For special experiments, such as observing Raman lines at extremely low frequency, a third monochromator may be needed. The light coming out the exit slit of the final monochromator is collected and focused on a photomultiplier tube, which converts photons of light into an electrical signal after amplification. For special purposes a pulsed laser is also used as a light source. Had the laser been invented 20-30 years earlier, the popularity of Raman and IR spectroscopy might have been reversed. In a modern Raman spectrometer, the Raman wave number (wave number difference of the incident and the scattered light) and the absolute value of the wave number of the scattered light are automatically shown on the instrument panel. For a liquid sample, a capillary tube is the most commonly used container. There are different devices for holding samples depending on the need. For instance, for deuterated samples, the author used a specially constructed sealed

r

~

FIGURE 2.6. A Raman spectrometer and computer attachment used at the author's laboratory at Colorado State University. (A) Ramalog 5 manufactured by Spex Industries. The laser tube is placed in the back and is not shown in the photograph. (B) Spex SCAMP computer. The computer can average spectra after repetitive scanning, calculate intensity ratios or the ratio of areas of two lines, and measure the depolarization ratio.

1;;1

\\11 I \ I \'.-1\C

> l-

e;; Z

\

'

~ z « :E «c::

~1!1j

I

W

I

~

II~

1700

\

l!l!t,'1

~ '~1 j

;,,1

1600

B

\ ~ All

! \ I

III

I

~ I l'll~ ~

I~I~ ~!lI!I.~ ~ I

~

'I

1\

"

~

J

A

I

i

1500

1400 -1

1300

1200

eM

FIGURE 2.7. (A) Raman spectrum of lysozyme obtained from one scan. (B) Additive spectrum derived from 10 scans registered in the SCAMP computer. (C) Averaged Raman spectrum of lysozyme derived from 10 scans with smoothing action. These spectra were obtained using a SCAMP computer in the author's laboratory.

r Special Techniques

53

glass chamber to prevent reexchange with moisture in the air. For Raman-intensity measurement at elevated temperatures, the author constructed a copper heating block that is connected to a rheostat to control the heat generation. The temperature of the block is read on a thermocouple (Fox and Tu, 1979). For colored samples or any that are ordinarily destroyed by absorption of heat from laser light, Raman spectra can be obtained by rotating the sample. A sample rotator attachment can be obtained from Raman-spectrometer manufacturers. Usually Raman signals are very weak, so background noise occasionally becomes high. Signal averaging with the aid of a computer can improve the quality of the signal-to-noise ratio. The author uses computer averaging routinely (Figure 2.7). Using conventional Raman spectroscopy, a relatively long time is required to obtain a complete spectrum. This limits the use of Raman spectroscopy to relatively stable molecules. Recently, because of technological advances, multiwavelength detectors have become available for Raman spectroscopy. With the combined use of a picosecond laser and multiwavelength detector, one can obtain Raman spectra of short-lived compounds. For instance, a 7-ns time-resolved resonance Raman spectrum of cytochrome c with good resolution was obtained by Woodruff and Farquharson (1978). Recently an optical multichannel analyzer with sufficient sensitivity has become available to Raman spectroscopists. It consists of a large number of detectors, with each detector "channel" measuring a different wavelength of scattered light. Since normal scanning method is time consuming, it is not suitable for a fast reaction. A multichannel analyzer records the frequencies and intensities of all scattered Raman bands simultaneously. Rotating choppers with variable-size slits are also frequently used for time-resolved resonance Raman spectroscopy. The choppers and a continuous-wave laser function as a pulsed laser with variable pulse width. 3.

SPECIAL TECHNIQUES

As Raman spectroscopy is advancing, many special techniques are becoming more common. In this section, a few of them are briefly mentioned. 3.1.

RAMAN 01 FFERENCE SPECTROSCOPY (RDS)

Double-beam spectrometers are extensively used in IR, visible, and UV absorption spectroscopy in order to cancel the absorption by water or solvent. Such a two-channel technique has just been introduced for Raman spectroscopy. Raman difference spectra are obtained by the use of a cylindrical cell with a .~.partition along a di~meter' so th~t two sample~ are alternately illuminated by . the laser as the ceills rotated (Kiefer, 1977) (Figure 2.8). The computer-generated difference between the Raman spectra of the two samples is plotted. By

54

The Laser Raman Spectrometer and Special Techniques RAMAN

DIFFERENCE

SPECTROSCOPY

CD

CD-® CYLINDRICAL ROTATING RAMAN SPUT CELL

q q

Q)® FIGURE 2.8. Simplified diagram of the arrangement for Raman difference spectroscopy. As the cell is rotated, a synchronous signal is sent to gating and counting electronic instruments to allow for the independent accumulation of data from each sample with subsequent independent storage in a computer. To obtain a difference spectrum, the intensity of a preselected Raman line in one spectrum is adjusted to equal the intensity of that line in the other spectrum. The two spectra are then subtracted digitally.

the RDS technique one can measure frequency differences as small as 0.02 cm- 1 between the maxima of very similar Raman bands of differen t compounds. An actual example of RDS on cytochrome c from tuna and horse is shown in Figure 2.9 (Shelnutt et al., 1979; Rousseau, 1981). Because of further technical improvements, four-channel Raman difference spectroscopy has been developed (Laane and Kiefer, 1981). 3.2. 3.2.1.

COHERENT ANTI-STOKES RAMAN SPECTROSCOPY (CARS) Technique

The CARS phenomenon was discovered by Terhune in 1965. Recently CARS has attracted great attention in biochemical research, because one can get Raman spectra free from fluorescence background.

....

Special Techniques

Tuna -

55

1.24 X Horse

~

i

'iii

c:

.•c:.. c:

II

E II

a:

780

720

800

FIGURE 2.9. Raman difference spectrum of tuna cytochrome c versus horse cytochrome c. The 750 cm - I line of tuna cytochrome c is 0.1 cm - I higher in frequency than that of horse cytochrome c. The figure was reproduced from Shelnutt et al. Proc. Natl. Acad. Sci. USA 76 (1979) by permission of the copyright owner, National Academy of Science.

CARS is based on the nonlinear conversion of two laser beams into a coherent laserlike beam of high intensity in the anti-Stokes region. The essence of this technique is that the sample is illuminated by two nearly colinear laser pulses with wave number "'I and "'2' The laser with wave number "'I (pump laser) is stationary in wave number, whereas the second laser, with wave number "'2 (probe laser), is scanned. When the value (2",. - "'2) becomes coincident with the wave number of anti-Stokes Raman scattering ("'3 = "'. + Il",), the light is emitted in the forward direction at wave number "'3' The emission is often many orders of magnitude greater than with normal scattering. This relationship is explained in more detail in Figure 2.10, using an energy diagram of illuminated light, emitted light, scattered light, and the energy level of the sample. The light "'3 emitted by the CARS process is identical to the normal anti-Stokes scattering effect "'3' These relations are summarized as follows: I.

The condition of illuminating by two lasers to produce the emitted light (Figures 2.1OA-F):

'" I + ("'. - "'2) = 2'" I - "'2

= "'I + Il", = "'3 2.

The condition to produce anti-Stokes Raman line (Figure 2.1OG):

"'. + Il",

= "'3

56

The Laser Raman Spectrometer and Special Techniques

CARS Effect:

6~E~~-=-~_~:

../\j. 6W-..,.t--

•

-~r- ~T:~­

±

.

--

B.

A.

C.

6~lT=== ,,

===·1-===

J\/.

WI

WI

i,

-e D.

iI

w?,= WI

+{),.W

_ F

E.

Romon Effect (Anti-Stokes Line):

:~!6W'~ •

The final result is F effect = G effect or CARS effect (W 3 )= Anti-Stokes effect (w 3 )

G.

FIGURE 2.10. Diagram illustrating the CARS effect and anti-Stokes Raman effect. By coincidence, the final results of the two processes have the same energy.

where ~W

=

WI -

W

z

Therefore, our main interest is not just to produce new emitted light - wz ), but to detect the light whose wave number is coincidentally identical to the anti-Stokes Raman line with wave number W 3 • The CARS spectrum is obtained by plotting the intensity of the emitted light against the frequency (or wave number) of scanned light W z or against ~w. In normal Raman scattering, anti-Stokes lines are weaker than Stokes lines because at normal temperatures the lower vibrational states of a molecule are more populated than the higher vibrational states. Under these conditions, more of the molecules in the population show the Stokes effect (for details, see Section 2.3, Chapter I). In the CARS process, the emission of light of

(2w I

~

Special Techniques

57

frequency identical to that of the anti-Stokes line is not subject to this rule and therefore has a higher intensity at normal temperatures. For biochemists the biggest attraction of this method is to obtain clearly resolved Raman spectra of biological samples without fluorescence interference. Readers are advised to see more-comprehensive reviews on this subject (Begley et aI., 1974; Hudson et aI., 1976; Nibler et aI., 1977; Long, 1977; Harvey, 1978; Morris and Wallan, 1979). CARS is not without technical difficulty (Tolles et aI., 1977). It is very critical to adjust the angles of the pump and probe laser beams properly. It also suffers from the presence of a large, broadbanded, nonresonant background signal (Wallan et aI., 1977; Morris et aI., 1978). 3.2.2.

Biochemical Application

Several compounds have been investigated by CARS. In resonance CARS, the spectrum is obtained in resonance with the electronic excitation. The intensity and shape of the CARS line depends on the frequency of excitation. For instance, the C= 0 stretching band of FAD (flavin adenine dinucleotide) appears at 1635 cm -I. As the excitation wI is changed from 485 to 525 nm, the shape of the 1635 cm- I line changes from positive Lorentzian through dispersion to negative Lorentzian (Dutta and Spiro, 1978). It has been difficult to obtain good spectra of certain compounds by conventional resonance Raman spectroscopy because of high levels of fluorescence. It is therefore quite an achievement that Raman spectra were obtained for FAD and glucose oxidase using the CARS technique (Dutta et aI., 1977; Dutta et aI., 1978). By this technique, even the spectrum of FMN (flavin mononucleotide) semiquinone was obtained, and it was shown that it is quite different and readily distinguishable from that of oxidized flavin (Dutta and Spiro, 1980). When coherent anti-Stokes Raman spectra of lumazine protein in the presence and absence of excess luciferase are compared, there are considerable differences in the 1264-cm -1 pyrimidine breathing mode, suggesting an interaction of lumazine protein and luciferase. Lumazine protein is a blue fluorescent protein isolated from the bioluminescent bacterium Photobacterium phosphoreum (Lee et aI., 1981). CARS spectra of cytochrome c and CO hemoglobin also show resonance Raman bands that are mainly of porphyrin vibration modes (Nestor et aI., 1976; Dallinger et aI., 1978). As the wavelength moves away from the absorption maximum, the inverse Raman effect takes place for cytochrome c and Vitamin B12 , and the dispersion curve becomes negative. This effect takes place when the solution is transparent at that wavelength (Nestor et aI., 1976). Figure 2.11 shows the CARS spectra of two compounds, light- and darkadapted bacteriorhodopsin (Tretzel and Schneider, 1979; 1980). CARS has also been applied to the interaction of acridine orange with DNA. The addition of the dye to DNA changes the CARS spectra, suggesting that the acridine orange intercalates into the spaces between the base pairs of DNA (Tretzel and Schneider, 1978).

58

The Laser Raman Spectrometer and Special Techniques

'"g.

CD N

1.0

!!!

!! ~

~Q.5 e

~ o o

2500

2000

1700 1500

Frequency (cm- I )

.:.~,.~.3.~.;r.~:.~~.~,;~ - ...~.~.·~~~,,~'t.~**.::,~.~./!:.:/~.tt'.;\··,.:.;·.;.;,>(R ef erence for {1-Turn

Brewster et aI. (1973), Ballardin et aI. (1978) Reed and Johnson (1973)

Xray

Rudkoand Low (1975)

X ray

Hodgkin and Oughton (1975), Stem et aI. (1968)

NMR

VenkatachaIapathi and BaIaram (1982) ShamaIa et aI. (1977) Prasad et aI. (1979)

TypeIlr BOC-Cys-Pro-VaI-Cys-CONHCH 3 I

I

S

S

Z-Aib-Pro-AibAla-COOCH 3 Z-Aib-Pro-CONHCH 3

aROC_

terti~rv hlltvlnxvr.~rhnnvl prnnn°

7.

1668

1267

1665

1265

1667

1286

hf"n7vlnYVr~rhnnvl arnl1n

Ishizaki et aI. (1982) Ishizaki et aI. (1982) Ishizaki et aI. (1982)

Xray Xray

78

Proteins

Experimental results are often within the range of calculated frequencies, most consistently for the amide I band (Bandekar and Krimm, 1979a, b; Krimm and Bandekar, 1980). For the amide III band, some frequencies fall within the calculated range, although none of the experimental data appear as high as 1300 cm -1 (Han et aI., 1980). Many amide III bands are actually lower than the calculated values. For gramicidin S, t,here are four amide III bands at 1240, 1258, 1273, and 1293 cm -1. The 1240-cm -1 band is associated with ,8-sheet structure, as gramicidin S is known to contain both ,8-sheet and ,8-turn structure. Pro-Leu-Gly-NH 2 is a carboxamide C-terminal tripeptide from oxytocin; the tripeptide is known from X-ray analysis to possess a type II ,8-turn (Reed and Johnson, 1973). With the exception of a band at 1238 cm- I , all band frequencies are close to the calculated values (Hseu and Chang, 1980; Fox et aI., 1981). It seems that there is a fairly wide range in values of the amide III band, but it is definitely higher than those of ,8-sheet and random coil. Thus Raman spectroscopy can provide diagnostic evidence for ,8-turn structures by careful analysis of both amide I and III bands. As more model compounds having ,8-turn are examined by Raman spectroscopy, more-precise information on the amide I and III band frequencies will be established. Although the Raman data on the ,8-turn are relatively few, the ranges of the amide I and III bands so far investigated are summarized in Figure 3.6. 2.1 .4.

Omega-Helix

Poly(,8-benzyl-L-Asp) can form the w-helix (left handed) from the left-handed a-helix by heating at 160°C under vacuum. The amide I band appears at 1675 cm- 1 in Raman and at 1676 cm- I in IR spectroscopy (Frushour and Koenig, 1975b). This is the only investigation on omega-helix; therefore, the correlation between Raman data and the omega-helix is not definite at this stage. 2.1.5.

y- Turn

The only y-turn-containing peptide investigated by Raman spectroscopy is [l-penicillamine]-oxytocin. This compound has been shown by nuclear magnetic resonance (NMR) to contain y-turn (Meraldi et aI., 1977). Therefore, it is premature to draw any definitive conclusions on its relationship to Raman data. For solid samples of [I-penicillamine] oxytocin, amide I and III bands appear at 1668 and 1255 cm- I , respectively. For aqueous samples, the amide I band appears at 1656 and 1666 cm ~ 1, whereas the amide III band appears at 1255 cm -1 (Hruby et aI., 1978). 2.2.

COMPARISON OF AMIDE I AND III BANDS

The amide III band is more sensitive to structural changes than the amide I band. Lysozyme has a-helix in residues 5-15, 24-34, and 88-96; antiparallel ,8-sheet in residues 41-45 and 50-54; and random coiled structure. These three different conformations are reflected in the amide III bands at 1272, 1238, and

Secondary Structure (Peptide-Backbone Structure)

79

1258 cm- I , respectively. However, only one distinct amide I band at 1660 cm- I can be observed (Yu and Jo, 1973a). The best and most accurate way to determine protein conformation is by the combined use of both amide I and amide III bands. It is risky to determine conformation based solely on the amide III band, since this region is a highly mixed vibration zone. The amide III band can be accurately determined by dissolving protein in D2 0 to allow isotopic exchange. The deuterated protein should give a new amide III' band in the vicinity of 980 cm -I, and any bands not shifted in the region of 1200-1300 cm- I are not amide III bands. The amide I band usually has less interference, but even so, the amide I band is an average over the different conformational distributions. For instance, the amide I band of native feather keratin can be resolved into two components (Hsu et al., 1976). With the simultaneous use of both amide I and III bands, it is possible to differentiate a-helix, ,B-sheet, ,B-turn, and random coil, where any structure that does not belong to the first three structures is grouped together as random coil, or disordered structure. These relationships are shown in Figure 3.6. a-Helix, ,B-sheet, and random-coil structures have been extensively studied by many investigators; thus good correlations exist between the Raman spectroscopic data and their respective structures. Only a few peptides with ,B-turn have been investigated by Raman spectroscopy. The investigation of more compounds is necessary to make more precise correlations between ,B-turn structure and the amide I and III band frequencies. Hydrogen bonding involving C=O exerts a great effect on the frequency of the amide I and III bands. When a peptide-bond C=O is involved in hydrogen bonding, it decreases the amide I band frequency, whereas it increases the amide III band frequency. Cis and trans amide bonds have different frequencies. In proteins all peptide bonds are in the trans form. Occasionally a glutamic acid residue at the N-terminal forms an amide bond to become a pyroglutamyl residue. In such a case, the amide bond is in the cis form. Thyroid releasing factor, a hormone, is a very interesting peptide from the viewpoint of the amide bond (Bellocq et al., 1973). The sequence is pGlu-His-ProNH 2 • As can be seen from the chemical structure, the hormone contains four amide bonds (Figure 3.9). One is the pyroglutamyl bond, which is in the cis form; the glutamyl-histidine bond is in the trans form; the histidyl-proline bond is an example of a tertiary amide bond, and the carboxy-terminal amide is a primary amide bond. The frequencies for these amide bonds are different and are shown here. Amide Bond cis-form amide trans-form amide tertiary amide primary amide

In H 2 O (cm- I )

In D 2 0 (cm- I )

1677 1660 1640 1677

1663 1640 1640 1640

80

Proteins pGlu-His-Pro NH

r--u---;

~2

0,... " ....C .{ I

Z

N~N

I

~2

I

" CH 2 CH2,.----' CI H2C/ II H, CH2 I I' I ,.---, ,.-----, 1 I ' N ;C 'c I 'C NH2: :______."' H...N....--CH-\Cr- C .11, H,,II - N I H..,II I

I

I'

'L 0 .J' cis form

trans form

I

'0

1.

I

",I

tertiary form

L .0

.JI

primary form

FIGURE 3.9. Structure of pGlu·His·Pro·NH 2 .

The cis-form and primary-amide-bond vibrational modes appear at the same frequency-1677 cm - 1 - by coincidence, and these are separated in DzO. The assignment was made from N-acetylprolinamide, which has bands at 1677 and 1615 cm- I • These bands shift to 1650 and 1610 cm- I in DzO. The 1677-cm- 1 band is assigned to the vibrational mode of the primary amide, and the band at 1615 cm- I to the tertiary amide in N -acetylprolinamide. 2.3. 2.3.1.

OTHER STRUCTURALLY SENSITIVE LINES

a-Helix

The amide I and amide III bands are sensitive to conformational changes in the peptide backbone. Besides these two bands, the 890-945-cm- I band is also sensitive to structural change. There is an a-helix line at 890-945 cm -I that disappears or displays weak intensity upon conversion to jJ-sheet or random coil (Frushour and Koenig, 1974, 1975b). Thus the 890-945-cm - I line is a characteristic Raman line for a-helical conformation. The band arises from the skeletal C-C stretching vibration. There is a wide range in the position of this line. For instance, for a-helical polypeptides of polY(L-Ala), it appears at 931 cm- I ; for polY(L-Lys), at 945 cm- I ; for polY(L-Leu), at 931 cm- I ; for poly(L-Glu), at 931 cm- I ; for polY(L-Met), at 907 cm- I ; and for poly(jJ-benzyl-L-Asp), at 890 cm- I . For a-helix of polY(L-Glu), the characteristic line appears at 924 cm- I (Fasman et a1., 1978a, b). Muscle is known to be rich in a-helical proteins that show a strong band at 939 cm -I with the amide I band at 1648 cm - I, which is a characteristic of the a-conformation (Pezolet et aI., 1978). One of the muscle components, tropomyosin, is known to have mainly a-helical structure. It too shows the characteristic a-helical C-C stretching vibration at 940 cm - I (Frushour and Koenig, 1974).

Secondary Structure (Peptide-Backbone Structure)

2.3.2.

81

,8-Sheet

, For the ,8-sheet, characteristic lines lie in the 1020-1060 cm ~ 1 region. For ,81-poly(L-Glu), the line appears at 1042 cm-I, and for ,82' lines appear at 1021 and 1059 cm - I (Fasman et a1., 1978b). The difference between ,81- and ,82-type conformations lies in the spacing distance of the hydrogen-bonded pleated sheets. The ,82-form is much shorter than the ,81-form as studied by X-ray diffraction, IR, and CD spectroscopy (Hoh et a1., 1976). 2.3.3.

C-H Stretching Vibrations and Conformation

The C-H stretching vibrations appear in the region of 2800-3000 cm- I . Structural implications of C-H bands to protein structure have not been extensively studied. However, there is an indication that some bands may indeed have structural implications. The 2930-cm - I band arises from the C-H stretching vibration of the CH 3 group. Unfolding of RNase produces a large increase in Raman intensity at 2930 cm ~ I. This is interpreted as the exposure of previously buried aliphatic amino acid residues to the surrounding water (Verma and Wallach, 1977). The ratio of integrated Raman intensities of C-Hand 0- H stretching bands of aqueous lysozyme solutions is related to hydrogen bonding or hydration between protein and water (Cavotorta et a1., 1976; Samanta and Walrafen, 1978).

2.4.

THE D- AND L-AMINO ACID COPOLYMERS

PolY(L-amino acid) has a tendency to form the right-handed a-helix. When L and D forms of amino acids are mixed to form a random copolymer, the a-helix is disrupted. As a matter of fact, polY(DL-Ala) in the solid state is more like the disordered-chain conformation, as indicated by its Raman data, shown here (Frushour and Koenig, 1975a):

PolY(L-Ala) PolY(DL-Ala)(powder)

Conformation

Amide I (cm ~ I )

Amide III (cm ~ I)

a-Helix Random coil

1656 1665 1674

1274 1242 1247

X-ray diffraction data indicate that polY(DI:-Ala) does not have significant a-helical content (Brown and Trotter, 1956; Arnott and Wonacott, 1966).

82

Proteins

2.5.

RIGHT AND LEFT-HANDED a-HELICES

A polypeptide that consists of nothing but L-amino acid residues forms a right-handed a-helix, and a polypeptide with only D-amino acid residues produces a left-handed a-helix. Raman spectra for the pure L- or D-poly( y-benzyl-Glu) are identical. However, the racemic (50:50 mixture) poly( y-benzyl-Glu) has small but definite spectral changes. It is known that side-chain interactions in the racemic mixture lead to small conformational changes. Therefore, the observed change in the Raman spectra for the racemic mixture is attributed to changes in side-chain conformation and very small changes in the backbone. The amide I peak is at 1650.5 cm- I, a shift of about - 5 cm -1, and the amide III peak is at 1291 cm- I , a shift of +2.5 cm- t (Wilser and Fitchen, 1974). 2.6. 2.6.1.

DEGREE OF POLYMERIZATION Synthetic Oligopeptides

The secondary structures of proteins and polypeptides have been extensively studied, but relatively little study has been done on linear oligopeptides. It is generally agreed that their structures vary with different side chains. Baron et al. (1979) investigated this problem using homooligopeptides of L-valine, L-isoleucine, and L-phenylalanine by IR and Raman spectroscopy. For the peptides with n > 4, the amide I band appears at 1655-1665 cm- I and the amide III band at 1215-1228 cm- I; these spectra are more like those of the ,8-conformation. X-ray data show that some dipeptides and tripeptides such as Gly-Gly, L-Ala-L-Ala, and (L-Alah have an antiparallel ,8-structure and AC-L-Ala-NHMe has a twisted antiparallel structure (Rao and Parthasarathy, 1973; Tokuma et aI., 1969; Fawcett et aI., 1975; Harada and litaka, 1974). All this evidence suggests that even small peptides can have ordered structure as solids. Raman spectra of some simple peptides such as Gly-Gly, (GlY)4' Ala-Gly, and Gly-Ala in water and deuterium oxide are catalogued in the paper of Lord and Yu (1970b). Those who wish to see these lines are advised to consult the original reference. Even small peptides may have their own specific conformation. For instance, N-acetylserine methylamide, N-acetyltyrosine methylamide, and Nacetylhistidine methylamide have different rotational isomers as shown by Raman spectroscopy (Koyama et aI., 1977). 2.6.2.

Synthetic Polypeptides

The conformation of certain synthetic peptides depends on the degree of polymerization. The conformation can be readily determined by the combined use of the amide I and III bands from Raman spectra. Poly(L-Val) has ,8-sheet

secondary Structure (Peptide-Backbone Structure)

83

structure, but as the degree of polymerization increases above 500, a-helical structure begins to form (Fasman et al., 1978a). This a-helical structure of polY(L-Val) is rather unstable. The a-helix can be stabilized by introducing a strong helix-former such as L-alanine into a copolymer. 2.7.

SOLID AND AQUEOUS PHASES

Because of the low intensity of the 0- H vibration, Raman spectroscopy is ideal to study conformation in aqueous solution. This is a particular advantage because it is in this medium that the majority of biological molecules exist. When one obtains a conformation from X-ray diffraction, one always wonders whether it is identical to that in aqueous solution. Since Raman spectra can be obtained from either solid or aqueous phases, Raman spectroscopy is a good tool with which to investigate this problem. The conformations of snake neurotoxins (Yu et al., 1975; Tu et al., 1976a), Mojave toxin from Mojave rattlesnake venoms (Tu et al., 1976b), oxytocin agonists and antagonists (Hruby et al., 1978), and apamin (Nurkhametov et al., 1981) are identical in solid and aqueous phases, as there are no significant changes in amide I and III bands. Glucagon, however, exists predominantly as a-helix in crystal form, whereas it exists as l3-sheet in gel, since it shows different amide I and III bands in the two phases (Yu and Liu, 1972b). With lysozyme, the amide I and III bands are identical for crystals and aqueous solutions, but there are many spectral changes at other frequencies. This is interpreted to mean that the main peptide conformation is the same between the two phases; however, there are some side-chain conformational changes (Yu and Jo, 1973a, b). The disulfide stretching vibration (500-550 cm -I) is frequently examined for clues of conformation change, since the disulfide bridge is very important in maintaining a particular tertiary structure of a protein. When rat-liver acid phosphatases I and III are dissolved in water, the S-S stretching vibration frequency changes from 515 to 506 and 505 cm -I, respectively. This reflects the fact that the geometry of disulfide bridges changes' from a solid-phase protein to an aqueous phase. This effect is a consequence of changes in the secondary and tertiary structures of the enzyme (Twardowski, 1978). Lyophilization is frequently used by biochemists in order to store protein in a powder form instead of keeping it in solution. From experience, biochemists know that some proteins subjected to this process retain full biological activities, whereas others lose activity completely. In order to see the effect of lyophilization, RNase was examined by Raman spectroscopy. There is a marked difference in the tyrosine doublet at 830 and 850 cm-) for the powder and aqueous solution. Such a difference is attributed to changes in the local environments of the tyrosine side chains (Yu et a1., 1972a; Yu and Jo, 1973a, b). This is clear evidence that lyophilization may change the protein conformation slightly.

84

Proteins

Raman spectra obtained from a single insulin crystal at two orientations give essentially identical spectra. Insulin fibrils of "wet" and "dried" samples, however, give different spectra, especially at 1227 cm -1, indicating that the loss of bound water or loss of the hydrogen bonding does perturb the protein conformation (Yu et aI., 1974). Amide I and III bands of a-lactalbumin crystals are essentially identical to those in solution, indicating that crystallization produces no detectable effect on backbone conformation. Lyophilizedpowder samples of a-lactalbumin show significant change in the amide III band, a clear indication of alteration in protein conformation upon lyophilization (Yu, 1974). In pancreatic trypsin inhibitor, the amide I frequency increases by 3 cm- I , and the amide III bands at 1238, 1263, and 1284 cm- 1 shift to slightly lower frequencies when lyophilized powder is dissolved in water. This is explained by a weakening of hydrogen bonds in the inhibitor protein when it dissolves in water. Since the relative intensities of the three amide III peaks are the same in the aqueous as in the powder form, the relative distribution of secondary structures remains the same for the powder and the aqueous-solution forms. The greatest changes are observed in Raman lines due to the aromatic-side-chain vibrations of tyrosine and phenylalanine, indicating that the microenvironments of aromatic groups are greatly altered by converting the solid phase to an aqueous phase (Brunner and Holz, 1975). 2.8.

EFFECT OF PROTEIN ON WATER

There are many studies of proteins in aqueous solution, but most studies are focused on the effect of water on the protein molecule itself. It is equally important to understand how a water molecule is affected by introducing a protein into water. At low protein concentrations there is no competition among protein molecules for their own water shell; however, at certain concentration values, competition will make probable a superposition of the hydration shells of different molecules (Cavotorta et aI., 1976; Aliotta et aI., 1981). One way to measure the effect of proteins on water molecules is to plot the I CHI I OH ratio (intensity ratio) against the protein concentration. The deviation from a straight line indicates interaction between protein and water molecules (Samanta and Walrafen, 1978). 2.9.

QUANTITATIVE ESTIMATION OF SECONDARY STRUCTURE.

So far we have discussed different types of protein conformations separately, but natural proteins are usually a mixture of the different conformations. Thus a method for determining the relative amounts of different secondary structures becomes important. The prediction of secondary structure from the amino acid sequence and CD is fairly common and has been applied to many proteins. Structure prediction based on Raman spectroscopy has not been extensively used since it

Secondary Structure (Peptide-Backbone Structure)

85

is a comparatively new technique. Pezolet et aI. (1976) proposed methods based on the position and intensity of the amide III band and CH 2 bending .vibration of proteins to quantitate secondary-structure forms from Raman . spectra. The validity of these two methods has not been widely established to date; however, successful results were obtained for human carbonic anhydrase B (Craig and Gaber, 1977), human immunoglobulin (Pezolet et aI., 1976), and sea snake neurotoxin (Fox and Tu, 1979). In Lippert's method (Lippert et al., 1976), a set of four simultaneous equations is used. They are obtained from Raman spectra taken in both H 20 and D20 and use the relative intensities of the amide I and III bands. The purpose of using 0 2 0 is to avoid the small influence of the water-molecule vibration on the amide I band. The amounts of various types of secondary structures can be obtained by solving the following simultaneous equations:

C proteinIProtein 1240

-

/, a 1240

R + J{3(I{31240 + J:R I 1240

C proteinIprotein 1632

-

/, I a a 1632

R + J{3( I{31632 + J:R I 1632

C proteinIProtein 1660

-

/, I a a 1660

R + J{3( I{31660 + J:R I 1660

fa

+ /p + fR

r

= 1

where fa' /p, and f R refer to the fractions of a~ helix, ,a-sheet, and random coil, respectively. The experimental values of I protem (intensity) are related to the I;, If, and I: intensities previously determined for poly (L-Lys) in its various secondary-structural forms. cprotein is a scaling constant that represents the relative intensity of the methylene band in the protein. As can be seen from these equations, they do not include a term for ,a-turn (,a-reverse turn) structure; therefore, the method gives the content of a-helix, ,a-sheet, and unordered structure only, without giving any information on ,a-turn content. The ,a-turn content is probably distributed to the unordered-structure (random coil) term in this method (Fox and Tu, 1979; Bailey et aI., 1979). Lippert's equation could become a better method for predicting protein structure if it were modified to include the ,a-turn structure. The secondary structure of human carbonic anhydrase B was estimated using the methods of Lippert et aI. (1976), and the result was compared with results from X-ray diffraction (Craig and Gaber, 1977). Remarkably close results were obtained: Raman

X-Ray*

Secondary Structure

(%)

(%)

a-Helix ,a-Sheet Disordered

19

17

39 42

40

'X-ray data was based on the work of Kannan et aL (1975).

43

86

Proteins

TABLE 3.5. Relative Intensity8 of the 1240-cm- 1 Amide III Raman Band and Fraction of ~-Structure for Different Natural or Synthetic Polypeptides

Protein or polypeptide Poly(L-Lys) Ribonuclease A Basic Pancreatic Trypsin Inhibitor a-Chymotrypsin Lysozyme IgG

Frequency (em-I)

Average number of CH z per residue

Relative intensity

Fraction of IJ-Structure

1240 1239

4.0 1.3

4.8 1.6

1.0 0.38

1242 1243 1238 1240

1.4

1.9

1.1 1.2 1.3

1.1

0.45 0.34 0.16 0.37

0.3 1.5

Source: The table was reproduced from pezolet et aI. (1976). "The relative intensity is expressed as the ratio of the peak height of the 1240-cm- 1 band to that of the 1450-cm- 1 band, times the average number of CH z per residue. The fraction of ,a-structure was obtained from the X-ray data.

The method of Pezolet and co-workers (1976) is to calculate the amount of l3-sheet structure using the relative intensity, which is the ratio of intensity at 1240 cm- I to that at 1450 cm- I multiplied by the average number of CH 2 group per residue, instead of using straight-intensities. They normalized intensities of the amide III band against the methylene-bending-vibration band at 1450 cm - I because of its insensitivity to structural change (Table 3.5). As they pointed out, this method can be applied only when there is a well-defined amide III band characteristic of the l3-sheet structure at 1240 ± 3 cm- I. Moreover, this method can be used only for the content of l3-sheet structure. The method is based on the fact that the fraction of l3-sheet structure has a linear relation to the relative amide III intensities of proteins with known l3-sheet content. By plotting a standard curve, one can estimate the l3-sheet content of a protein one wishes to examine. The proteins used to construct straight-line curves are POlY(L-Lys), RNase, trypsin inhibitor, a-chymotrypsin, lysozyme, and IgG, which have l3-contents of 1.0, 0.38, 0.45, 0.34, 0.16, and 0.73 fraction, respectively.

3.

SIDE CHAINS

Unlike CD, Raman spectroscopy can be used to study the microenvironment of certain side chains. Often different biological properties of proteins are determined by the presence of certain side chains; therefore, it is important to understand the microenvironment of the side chains.

Side Chains

3.1.

87

TYROSINE

Yu, N.-T. et aI. (1973) found that the relative intensities of the Raman bands at 830 and 850 cm -1 are related to the environment of the tyrosine side chain. On some occasion~, the frequency of 860 cm - I has been reported instead of 850 cm-] (Bicknell-Brown et aI., 1981). Working with the dipeptide Gly-Tyr as an example of an exposed tyrosine, they found that the intensity of the 850/830-cm- 1 bands is 1/0.71 (Figure 3.10). An enzyme, RNase, is known to have a "buried tyrosine residue," and the intensity ratio is 0.8/1.0. On heating, the protein unfolds, thus exposing the tyrosine residue, and the 850-cm- 1 band becomes more intense than the 830-cm -] band. According to the investigation of Siamwiza et aI. (1975), the 850 and 830 cm-] doublet bands are due to Fermi resonance between the ring-breathing vibration and the overtone of an out-of-plane ring-bending vibration of the parasubstituted benzenes (Figure 3.11). If the tyrosine is buried, it acts as a strong hydrogen-bond donor; the ratio of 850/830-cm -] bands is about 0.5, resulting from the higher intensity of the 830-cm -I band (Figure 3.12 right). When the tyrosine is on the surface of a protein in aqueous solution (exposed), the ratio is higher because of the higher intensity of the 850-cm- 1 band (Figure 3.12 left). Using this property, one can quantitatively determine the number of buried and exposed tyrosine residues by using the following equation (Craig and Gaber, 1977). One should be

853cm- 1

82~ Gly-Tyr

)

l 853

830 830

RNase

3O.lamu- I /

2

0

OH

-0.257

•

CH 3

FIGURE 3.11. Vibrational modes of p-cresol as a model for the tyrosine residue. The figure was reproduced from Siamwiza et al. (1975) by permission of the copyright owner, American Chemical Company.

~~

(EJ llAJ em

em

H 0. 2

C'' "'©.:P'"."0·" 0 .. ·.,

"2°

",

IIp-osed Tyrosine Hydrogen Bond Acceptor and Donor

I

"

"Buried" Tyrosine Hydrogen Bond Donor

FIGURE 3.12. Raman doublet for the tyrosine ring. The intensity ratio of 830 to 850 cm- I is frequently used to determine whether the tyrosine residue is buried or exposed. The ratio depends on the manner of hydrogen bonding of the tyrosine hydroxyl group.

DD

Side Chains

89

careful with the equation originally shown in their paper because it had errors which are corrected here:

N buried O.5Nburied

+ Nexposcd = 1

+ 1.25Ncxposed = 1850/1830

For instance, human carbonic anhydrase B has a total of 8 tyrosine residues and the Raman intensity ratio of 850/830-cm - I bands is 0.9. Therefore, the above equation becomes N buried

0.5Nburicd

+ Nexposed =

+

1.25Nexposcd

1

= 0.9

where Nburied and Nexposcd refer to the mole fractions of buried and exposed tyrosine residues. Solving these equations, the values are Nburied = 0.46 and Nexposcd = 0.54. The values correspond to 3.7 moles of buried tyrosine and 4.3 moles of exposed tyrosine residues. X-ray diffraction studies indicate that the number of buried tyrosine residues is 4, and 4 are exposed (Kannan et aI., 1975). The two methods give excellent agreement. Sea snake neurotoxins have one tyrosine residue (Tu, 1973). Iodination of the neurotoxin gives only an 84% reaction even with an excess of 12 reagent, and nitration is only 50% complete (Raymond and Tu, 1972). This leads to the conclusion that the tyrosine residue in the neurotoxin is "buried" or "masked." Later studies of various sea snake neurotoxins by Raman spectroscopy revealed that the single tyrosine residue is, indeed, buried (Yu et aI., 1975; Tu et aI., 1976a). There is a change in the tyrosine vibrational bands when a tyrosine residue is involved in binding. A protein called LIV-protein specifically binds to leucine, isoleucine, or valine, causing a spectral change in the Raman frequencies for the aromatic residues, tyrosine and tryptophan (Vorotyntseva et aI., 1981). This illustrates the usefulness of the Raman technique in observing the microenvironment of tyrosine residues in a protein. 3.2.

TRYPTOPHAN

The characteristic bands of the tryptophan indole-ring vibrations appear at 544, 577, 761, 879, 1014, 1338, 1363, 1553, and 1582 cm- I (Lord and Yu, 1970b). Among these lines, the 1363-cm- 1 band can be correlated with the environment of the indole side chain. A sharp, intense Raman line at 1360 cm- 1 is diagnostic for a buried tryptophan (Yu, 1974). In carbonic anhydrase B, three residues are buried, and two residues are partially exposed, as studied by X-ray diffraction (Kannan et al., 1975). Raman analysis indicates that some

90

Proteins

of the residues are buried. The application of this method is also shown with sea snake neurotoxins, which have one tryptophan residue (Tu, 1977). The tryptophan residue in the neurotoxins can readily be modified by different chemical reagents, indicating that the tryptophan is exposed (Tu and Toom, 1971; Tu et aI., 1971; Tu and Hong, 1971). The Raman spectra of different sea snake neurotoxins indicate that the tryptophan is indeed exposed, because there are no 1360-cm- 1 lines (Yu et aI., 1975; Tu et aI., 1976a).

3.3.

PHENYLALANINE

The breathing vibration of the benzene ring of phenylalanine can be detected at 1005 cm -1 when the concentration of phenylalanine is above 1%. Although there is no particular band that can be correlated to the environment of the phenylalanine side chain in a protein, the ratio of phenylalanine to tyrosine can be determined. Yu and East (1975) estimated the phenylalanine-to-tyrosine ratio in lens proteins by comparing the intensities at 624 cm -1 (phenylalanine) and 644 cm- 1 ( tyrosine). When this method is applied to carbonic anhydrase B, the ratio is 1.4, which is in good agreement with the ratio (1.38) determined from the amino acid composition (Craig and Gaber, 1977). This method is based on the Raman intensity ratio multiplied by the factor 1.25: /624 /644

X

Phe 1.25 = Tyr

In order to check the validity of this method, 64 Raman spectra of 25 proteins were analyzed (Liddle and Tu, 1981). Of these, 28 out of 64 (44%) showed a positive correlation within a range of ±25% error. The results of this investigation indicate that the intensity-ratio method is of limited use for all proteins. Ribonuclease has three phenylalanines out of a total of 124 amino acids. Vibrational bands that originate from the phenylalanine ring can be seen in the Raman spectrum of RNase (Lord and Yu, 1970a). The aromatic-vibration bands are relatively insensitive to the state of aggregation. The lines due to the phenylalanine ring are summarized here: 622 Weak 1006 Strong- "breathing" vibration of the monosubstituted ring 1033 Weak 1183 } 1207 1585 These lines are overlapped when there are tyrosine residues 1605

Side Chains

3.4.

91

HISTIDINE

The imidazole group of histidine has two tautomeric forms (Figure 3.13). Tautomer I represents the I-N-protonated form, and II is for the 3-N-protonated form. The two forms show different breathing vibrations, which appear at 1282 cm- 1 for tautomer I and 1260 cm- I for tautomer II. The Raman spectrum obtained at neutral pH indicates that the imidazole group exists in an equilibrium between the two tautomeric forms (Ashikawa and Itoh, 1979). 3.5.

DISULFIDE BOND

Disulfide bonds (disulfide linkages, disulfide bridges) help to provide additional stability to a protein molecule. Clearly, understanding disulfide bonds in a protein is quite important to the structural study of proteins. Raman spectroscopy can be used for this purpose, furnishing information that other physical methods cannot. Raman spectroscopy shows a strong S-S stretching vibrational band in the region of 500-550 cm- I . The origin of the S-S stretching vibrations has been extensively studied. It has been found that the S-S stretching vibration depends on the internal rotation about the C-S and C-C bonds of C-C-S-S-C-C. A disulfide bond is normally expressed as -S-S(Figure 3.14) but more strictly speaking, it is C(a)-C(jJ)Hz-S-Sc(,B)Hz-C(a). The C(a) refers to the a-carbon atom to which peptide bonds attach. As elucidated from studies of many disulfide model compounds of known conformation, the symmetrical-stretching vibration of the disulfide bond is influenced by the conformation of the carbon atoms in the disulfide bridge Ca-Cp-S-S-Ca,-Cf/" The vibration at 510 cm- I can be assigned to the gauche-gauche-gauche (g-g-g) conformation (Figure 3.15). The gauche-gauchetrans (g-g-t) rotamer gives the band at 525 cm -1, and the trans-gauche-trans (t-g-t) at 540 cm- 1 (Sugeta et aI., 1972, 1973). Many naturally occurring proteins give the disulfide stretching vibration at or near 510 cm -(, suggesting that the gauche-gauche-gauche form is the most preferred conformation. Even when proteins are denatured by heat treatment, very little change in the H

H

I

I

~~'N;,H a

N

\4

1,

5

C=C'H I R

Tautomer J

--+ +--

C

H'N .... 2~N

a

1

\4

5

1

C=C'H I R

Tautomer II

FIGURE 3.13. Tautomerism of the imidazole ring of histidine.

92

Proteins

o

II

~

-N-CH- C - - H I CH 2

I

}

S

I

s

o II

I

CH 2

I

- C - CH -

FIGURE 3.14.

NH

-

Disulfide bond in protein.

intensity of the 510 cm- I band is observed. Occasionally new shoulders appear at 525 or 540 cm - I upon heat denaturation, suggesting that trans-gauche-gauche and trans-gauche-trans forms are formed in addition to the original gauchegauche-gauche conformation (Tu et aI, 1976a). However, other conformations are common among synthetic cyclic compounds such as [I-penicillamine]oxytocin and [I-penicillamine, 2-leucine]oxytocin (Hruby et al., 1978). Naturally occurring cyclic peptides such as mesotocin and

FIGURE 3.15. Dependence of the S-S stretching frequency on the internal rotation. (A) Gauche-gauche-gauche form, (B) gauche-gauche-trans form, (C) trans-gauche-trans form. Trans and gauche refer to the atoms from the left sides.

Side Chains

93

: argininylvasopressin have trans-gauche-trans conformation in addition to the .gauche-gauche-gauche form (Tu et aI., 1979). Occasionally the S-S stretching vibrational frequency appears somewhere other than at 510 cm- 1 for natural proteins. For instance, the Bence-Jones protein has one S-S vibrational band at 524 cm -1, indicating the transgauche-gauche type (Kitagawa et aI., 1979), and a sulfide band appears at 521 cm - 1 for pepsin (Tobin, 1968). In lysozyme and snake neurotoxins, only one intense disulfide stretching vibration was observed at 510 cm -I, suggesting that all the disulfide linkages have a similar local geometry. Insulin is an interesting example, because it has different types of disulfide bonds. It has two interchain and one intrachain disulfide bonds; there are two different disulfide Raman bands, one at 505 cm -I and the other at 517 cm- I. Moreover, the intensity ratio of these two bands is about 2 to 1. The same ratio is obtained from the C-S stretching vibrations at 668 and 680 cm -I. Since insulin does not contain methionine, the observed C-S bands are all from C-S-S-C of the disulfide linkages (Yu et aI., I972b). The S-S stretching vibrational band is rather prominent in Raman scattering, and often the appearance and disappearance of this band are correlated with a structural change in proteins. RNase has four disulfide bonds and upon reduction is converted to random coil. The disulfide-bond vibration at 516 cm- I reappears in the correctly refolded RNase (Galat et aI., 1981). The coagulation of egg white by heating is often thought to involve the formation of a disulfide bond. However, no band appeared in the 510-cm- 1 region when egg white protein was aggregated (Painter and Koenig, 1976c). Therefore, it can be concluded that no disulfide bonds are formed by the coagulation of egg white. 3.5.1 . Theory Proposed by Sugeta

Sugeta and co-workers (Sugeta et aI., 1972, 1973) proposed that the S-S stretching frequency does not depend on the C-S-S-C dihedral angle, but depends on the torsional angles in C-C-S-S-C-c. According to this theory, Raman spectroscopy can distinguish three types of disulfide-bond geometry, namely, gauche-gauche-gauche, trans-gauche-gauche, and transgauche-trans conformations (Figure 3.15). The Raman band appears at 510 cm - I for the g-g-g, 525 cm - I for the t-g-g, and 540 cm - I for the t-g-t conformation of C-C-S-S-C-c. There is some experimental evidence to support this theory, as shown in Streptomyces subtilisin inhibitor and lysozyme (Satow et aI., 1980). Lysozyme has three disulfide linkages at the positions Cys(6)-Cys(l27), Cys(30)-Cys(115), and Cys(64)-Cys(80), all with the g-g-g conformation, and one disulfide at Cys(76)-Cys(94) with the t-g-g conformation, as deduced from X-ray crystallographic analysis (Blake et aI., 1967). Raman spectra of lysozyme have one prominent peak at 507 cm- I for g-g-g and a smaller band at 528 cm- I for t-g-g (Nakanishi et aI., 1974).

94 3.5.2.

Proteins

Theory Proposed by Van Wart

The essence of this theory is that the S-S stretching frequency has a linear correlation with the C-S-S-C dihedral angle (Van Wart et al., 1973; Maxfield and Scheraga, 1977). Martin (1974) reported that there is no such correlation. After reevaluation, both Van Wart and Martin (Van Wart et al., 1976) agreed that the S-S stretching frequency is invariant to the C-S-S-C dihedral angle in the 65-85° range, but the frequency of the S-S vibration does vary with the C-S-S-C dihedral angle between 0 and 65° as originally proposed by Van Wart et al. In proteins, the S-S stretching frequencies quite often appear at 510, 525, and 540 cm- I. Van Wart and Scheraga ( I 976a, b) summarized the relationship between the S-S stretching frequencies and the C-C-S-S and C-S-S -C dihedral angles. These results are shown here:

"s-s (em-I) 510 ± 5 525 ± 5 540 ± 5

Dihedral Angle of C-C-S-S (deg)

Dihedral Angle of C-S-S-C (deg)

50-180 50-180 0-50 50-180 0-50 0-50

85 ± 20 85 ± 20 85 ± 20

According to the study of Van Wart et al. (1976), the band at 525 cm- 1 is not due to the trans conformation of C-C-S-S in C-C-S-S-C-C, but rather to a low value of the C-C-S-S dihedral angle. Similarly, the band at 540 em -I is considered to be associated with the trans-gauche-trans conformation of the C-C-S-S-C-C unit by Sugeta et al. However, according to Van Wart and Scheraga (1976) a value for "s-s of 540 cm- I arises from the presence of conformations with small C-C-S-S dihedral angles of about 30°. Thus there are two opposing theories concerning the origin of the S-S stretching vibration. 3.6.

C-S

Methionine and cystine residues have a C-S stretching vibration. There is a correlation between the C-S stretching frequencies and the internal rotation about the C-S bond in methionine and isobutyl methylsulfide (Nogami et al., 1975). This relationship is illustrated in Figure 3.16. The C-S stretching

'.'

\";

/CMETHIONINE RESIDUE

'Vk'

}t~

·.tl~'

,


+

. Papal n-SH

5 II

FIGURE 4.3. Dilhioacyl compounds can also be used as substrates for papain. The - C - 5 group is a cbromophore that can be resonance enhanced.

1.2.

CHYMOTRYPSIN

In proteolysis by chymotrypsin, a serine residue of the enzyme is involved in catalysis. The same reagents used for papain can be used with resonance Raman spectroscopy for elucidation of the mechanism of chymotrypsin catalysis (Carey and Schneider, 1974, 1976; Phelps et al., 1981). For this study, 4-amino-3-nitrocinnamoyl ester is used as a substrate, and the cinnamoyl group is covalently attached at serine-195 of a-chymotrypsin (Figure 4.4). The spectrum of the acyl enzyme ES shows absorption at 280, 340, and 430 nm. The 280-nm peak is due entirely to chymotrypsin, whereas the other two peaks are due to the enzyme-bound substrate. Therefore, resonance Raman spectra can be obtained using an excitation laser wavelength of either 340 or 430 nm. Similarly, 2-hydroxy-3-nitro-a-toluyl ester can also be used as a substrate to make the corresponding acylchymotrypsin. At pH 3, there is no change in the resonance Raman spectra of ES and S. Thus at pH 3 the conformation of the acyl group in the active site is not perturbed by forming an intermediate complex. At this pH, chymotrypsin is inactive, and the acyl enzyme ES is stable for days. However, on raising the pH to 7.0, the enzyme becomes active. The acyl enzyme at this pH has a

Enzyme Action

121

1 1625cm

H2N~CH=CH-COOR

+ HO-Ser-a-Chymotrypsln

N02

S

I

E -ROH

H2N.p-eH=CH-COO -Ser-a- Chymotrypsin N0 2

E-S H 20

H2N"9-CH=CH-COOH

+ HO-Ser-a-Chymotrypsln

N0 2

P

E

FIGURE 4.4. Enzymatic reaction scheme of hydrolysis of 4-amino-3-nitro-trans-cinnamic acid S catalized by chymotrypsin E. Using a resonance-Raman-active chromophore in the substrate, one can study the mechanism of an enzyme reaction by means of resonance Raman spectroscopy.

half-life of seconds. At an active pH, there is a drop in the intensity of the 1625 cm- I band due to the C=C stretching vibrational mode. Thus it can be concluded that twisting occurs about the C=C-C=O single bond in the catalytic process. In other words, distortion takes place in the bond near the linkage undergoing cleavage as shown here:

o II C=C-C- OR i i twist cleavage

1.3.

CARBOXYPEPTIDASE A

Many azo compounds are known to bind to proteins; these bindings can be studied by resonance Raman spectroscopy (Kim, 1975; Thomas and Merlin,

122

Enzymes and Immunoglobulins

1979). When azo compounds bind to enzymes, this allows the study of the enzymes' catalytic mechanisms. Carboxypeptidase A is a metalloenzyme containing zinc. Chemical modification of the enzyme with diazotized p-arsanilic acid (Figure 4.5) modifies tyrosine-248 with retention of catalytic activity. Since the reagent contains the azo group, -N=N-, the binding of the reagent to the enzyme generates a visible chromophore that can be studied by resonance Raman spectroscopy, since it shows a band at 1400-1500 cm- 1 (Lorriaux et al., 1979; Merlin and Thomas, 1979). On complexing, the bands responsible for C-O and N=N groups are shifted or changed in intensity. From these results, it is proposed that the microenvironment of the carboxypeptidase-arsanil complex in the active site is as shown in Figure 4.5. The same technique was applied to aldolase to make resonance-Raman-active azoaldolase (Masetti et al., 1976). The azo group is in the trans conformation, as this gives the - N = N stretching mode at 1440 cm-], whereas in the cis form the band appears at 1500 cm- I . The fact that complex formation decreases the N=N stretching vibration at 1440 by only 4 cm-] implies that the interaction of Zn(II) with the N=N group occurs through a lone pair of electrons rather than through a 'IT-orbital (Scheule et al., 1977, 1979). Crystal and aqueous samples of azocarboxypeptidase show different resonance Raman spectra at N=N (1380-1450 cm -]) and N -If> (1150-1210 cm-]) stretching vibrations, suggesting they have different azo Tyr-248 structure in the two phases. In aqueous solution, phenolic oxygen ionizes, depending on pH. In crystals, the phenolic proton of Tyr-248 is involved in an intermolecular hydrogen bond to a protein group. This interaction may be related to the marked reduction of the enzyme's activity brought about by crystallization (Scheule et al., 1980). Methyl orange binds to bovine serum albumin, and the azo group in this complex is also in a

9"'

N L--o-N

zn[:I[),

-

o

~

CH2

!J

~ ~ ~ .. ~~

FIGURE 4.5. Structure of the azotyrosyl(248) zinc complex of arsanilazotyrosyl(248)-carboxypeptidase A deduced from its resonance Raman spectra. The figure was redrawn from Scheule et aI. (1977).

Enzyme Action

123

trans conformation, as the N =N stretching vibration bands appear at 1415 and 1423 cm- 1 (Carey et al., 1972; Kim et al., 1975). It is, therefore, the trans conformation that is the likely structure in a complex involving the azo group. The distribution of the hydrogen-bonding system of azotyrosine-248 in water is perturbed by many inhibitors (Scheule et al., 1981). 1.4.

PEROXIDASE

The ES complex is the intermediate compound before a product is formed in an enzyme-catalyzed reaction. Yet the identification of this intermediate complex is usually very difficult because of the unstable nature of the complex. Peroxidase catalyzes the conversion of hydrogen peroxide to water in the presence of a hydrogen donor: H 20 2

+ AH 2 -> 2H 20 + A

The reaction proceeds through intermediate compounds I and II. It is known that horseradish peroxidase forms a stable intermediate complex in the absence of a hydrogen donor. The reddish brown color of peroxidase solution becomes olive green with the addition of H 20 2 (compound I or complex I), then it turns to pale red (compound II or complex II). Compound II accepts hydrogen from a donor, AH 2 , and eventually produces water. H 20 2 + 1ePeroxidase Compound I Compound II (Fe3+) 1AH 2 +le2H 20

(Fe3+ ) Resonance Raman spectroscopy can be used to study the intermediate compound I. The spectra of peroxidase and compound I are indeed different, indicating that the addition of hydrogen peroxide significantly alters the heme 7T-ring system (Woodruff and Spiro, 1974). The oxidation-state marker at 1382 cm-\ can be seen, but the Fe-O band observed in hemoglobin cannot be observed in compound II (Rakshit et al., 1976). Like peroxidase, myoglobin can form a stable complex with hydrogen peroxide. The resonance Raman spectrum indicates that the iron atom in the complex is formally in the Fe(IV) state with a low spin configuration (Campbell et al., 1980). 1.5.

THYMIDYLATE SYNTHETASE

Before a product is formed from a substrate, the intermediate complex ES is first produced. It is always curious to know whether there is any change in

124

Enzymes and Immunoglobulins

conformation of an enzyme when it forms a complex with a substrate. Raman spectroscopy can be used to study this as long as the amide I and III bands are not masked by the vibrational bands from the substrate moiety. The reaction catalyzed by thymidylate synthetase is as follows: thymidylate synthetase Deoxyuridate + 5, lO-methylenetetrahydrofolate - - - - - - - thymidylate + dihydrofolate 5, lO-Methylenetetrahydrofolate serves as a coenzyme in the reaction. In this case the intermediate is a ternary complex of the enzyme-substrate-coenzyme. The enzyme itself gives the amide I band at 1655 cm- I with a shoulder at 1680 cm- I . Upon forming a ternary complex, the amide I band remains at 1678 and 1660 cm -I. This is interpreted to mean that no change occurs in the overall secondary structure on formation of the ternary complex (Sharma et aI., 1975). Unfortunately, in these experiments the amide III band of the enzyme was not clear; thus they could not use the amide III band to verify this conclusion. 1.6.

OTHERS

Resonance Raman scattering can be observed when p-nitrophenylphosphate is mixed with rat-liver acid phosphatase, because they form a complex. It seems that histidine and aspartic acid residues are involved in the formation of the enzyme-substrate complex (Twardowski and Proniewicz, 1980). Alcohol dehydrogenase catalyzes the following reaction: -CHO

+ NADH + H+

--. -CH 2 0H

+ NAD+

During the formation of the ternary complex of enzyme-substrate-coenzyme, zinc is involved, as the Zn(II)-O stretching band at 363 cm -1 can be observed (Jagodzinski and Peticolas (1981). Because of recent technological advances in laser tubes, one can obtain a laser in the near-ultraviolet range (325-360 nm). Therefore, the furylacryloyl and the thienylacryloyl group can be attached to chymotropsin. From such resonance-Raman-active chromophores, the detailed structural aspect of enzyme-substrate intermediates can be studied (MacClement et aI., 1981). Glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidative phosphorylation of D-glyceraldehyde-3-phosphate to 1, 3-diphosphoglycerate in the presence of NAD+ via the formation of a covalent acyl-enzyme intermediate in which the acyl group is linked to the sulfur of an active-site cysteine. The compound ,B-(2-furyl)acryloylphosphate (FA) can be used as a substrate analogue, and this compound is resonance enhanced. The enzyme is composed of four identical subunits, and the resonance Raman spectra of FA-enzyme indicate that the complex exhibits heterogeneous binding in the active site (Storer et al., 1981).

Enzyme-Inhibitor Complexes

2.

125

ENZYME-INHIBITOR COMPLEXES

Inhibitors are frequently used to study the mechanism of enzyme reactions, as they sometimes bind to the active site of the enzyme. Unlike the enzyme-substrate complex, the enzyme-inhibitor complex does not undergo further reaction to produce a product and regenerated enzyme. Thus it offers a unique opportunity to study the active site of an enzyme or mechanism of an enzymatic reaction. Raman spectroscopy can be used for the mechanistic study of enzyme -inhibitor reactions. 2.1.

CHYMOTRYPSIN

2-Phenylethane-boronic acid-a-chymotrypsin complex will be used as an example. The inhibitor shows a 685-cm -I band at pH 11 and a 775-cm -I band at pH 5.0. The first band is characteristic of tetrahedral boron, whereas the second is characteristic of trigonal boron. The enzyme-inhibitor complex does not show the 685-cm -1 band, indicating that boron remains in the trigonal form. The inhibition is pH dependent, and this occurs in a subsequent step that leads to a tetrahedral adduct between enzyme and inhibitor, and also gives rise to a 684-cm- I band. Thus Raman spectroscopy shows that inhibition occurs in two steps (Hess and Seybert, 1975).

2.2.

CARBONIC ANHYDRASE

Carbonic anhydrase is a zinc metalloprotein that is strongly inhibited by aromatic sulfonamides. Zinc is essential for enzyme activity. X-ray studies have indicated that the zinc atom is located in a deep crevice that constitutes the active site, and it is coordinated to three histidyl side chains and a water molecule (Liljas et aI., 1972). The sulfonamide inhibitor binds to the enzyme very strongly and forms a very stable complex with a stability constant as high as 10 9 • A possible mechanism of the inhibition by sulfonamide is by blocking the active site of zinc, as shown in Figure 4.6. The binding site of the enzyme-inhibitor complex was studied by resonance Raman spectroscopy. Most unconjugated proteins are resonance Raman inactive. However, by introducing certain chromophore groups into a protein, one can convert resonance-Raman-inactive proteins into active ones. Figure 4.7 shows the compounds attached to enzymes by Kumar et ai. (1974, 1976).

0<Ei

;

-§-NH .....Znlnl, II

o

FIGURE 4.6. Mechanism of sulfonamide inhibition of carbonic anhydrase activity.

126

Enzymes and Immunoglobulins

The compounds I, II, and III all contain sulfonamide groups, as shown by the dotted lines. At the same time they contain an azo group that produces a resonance Raman effect. Resonance Raman study indicates that there is a change in geometry about the sulfonamide sulfur atom when forms enzymeinhibitor complex. From this finding it is postulated that inhibition may be due to the influence of the bound sulfonamide group, which closely mimics the transition state of the reactants in the reversible hydration of CO2, An increase in the frequency of the 1139 (I) and 1131 (II) cm - I bands upon binding and ionization strongly suggests that the bound sulfonamide group is present as S02 NH - . However, a different explanation was offered by Petersen et al. (1977). They concluded that the sulfonamide was bound to the enzyme as -S02NH2 rather than as -S02NH- . Moreover, they concluded that the sulfonamide is bound to the enzyme surface in the acidic (protonated)-S02NH2 form. The Raman spectrum of Neoprontosil (sulfonamide 4'-sulfamylphenyl-2-azo-7-acetamidoI-hydroxynaphthalene-3, 6-disulfonate) bound to the enzyme at pH 9.5 shows a shift in the intense -N=N stretching mode from 1414 (free) to 1407 cm- 1 (bound), suggesting that a slight conformational change about the -N=N single-bond linkage occurs upon binding (Carey and King, 1979). In order to clarify this discrepancy, cadmium-substituted carbonic anhydrase and 15N_ enriched sulfonamide were used by Evelhoch et al. (1981). The result indicates that aromatic sulfonamides, which inhibit carbonic anhydrase, are found with the ionized sulfonamide moiety. They concluded that the report of Peterson et al. (1977) is based on the misassignmen t of the band at ~ 900 cm- I. A

L1 ~~;~~1 -ow"'::::-'" ...:'."";

(C"l,N

II

r~"

"2

'y' --.~~??~

IN ·.. ···_·r··_ZtJ.:i ~

0

N

A

! : ' ; ' S()I~~: III

resona

active c~ce Raman romophore

:~~~c~~st~Oe ~~i~~ enZ)1TIe Sulfonar.l1de

FIGURE 4.7. Structures of three inhibitors of carbonic anhydrase action. Each compound contains a resonance-Rarnan-active chromophore and the enzyme attachment site. (I) 4sulfonamido-4'-dimethylarninoazobenzene; (II) 4-sulfonarnido-4'-hydroxyazobenzene; (Ill) 4sulfonarnido-4'-aminoazobenzene.

)· :{ I

-!- '/

;m>' Enzyme-Inhibitor Complexes

CI

-0-

~ + ,..~~N=N~ NICH 3)2

NH 2 ,

-

NH

FIGURE 4,8.

127

2

Structure of the trypsin inhibitor 4-amidino-4'-dimethylaminoazobeDzene.

comparison of the pH dependence of the resonance Raman spectra of sulfanilazocarbonic anhydrase with pH dependence of the spectra of sulfanilazotyrosine, sulfanilazohistidine, and sulfanilazotryptophan suggests that histidine is the site of modification of the carbonic anhydrase derivative (Li et aL, 1979). 2.3.

TRYPSIN

4-Arnidino-4'-dimethylarninoazobenzene is a competitive inhibitor of trypsin (Figure 4.8). The binding of the inhibitor to a specific pocket of the enzyme narrows the band widths compared with those found with free inhibitor. This can be explained by the freezing of the rotational motions of the inhibitor molecule (Dupaix et al., 1975). This interpretation is in agreement with crystallographic results (Krieger et aL, 1974). Studies of spin-labeled trypsin have shown that the mobility of the labels was decreased when bound to the protein (Berliner and Wong, 1974). 2.4.

OTHER ENZYMES

Zinc ion is required for alcohol dehydrogenase action. Zincon is a dye that forms a one-to-one complex with zinc, and is a coenzyme-competitive inhibitor (Figure 4.9). Since zincon contains an azo group, the binding of zincon to liver alcohol dehydrogenase can be studied by the resonance Raman technique. When the enzyme-inhibitor complex is formed, there are significant changes in the Raman bands at 1500, 1272, and 1100 cm -1, suggesting that zincon is

~

H03S'(jl

yOH

yCOOH

N':::::-N

,...NH ,

~N

C

6 Zineon

fIl

H03S~ y~, 09C~

Znltll

zn

N'::::-N N/NH . , ~

C

6 Zn-zineon

FIGURE 4.9. Structure of zincon, which is a competitive inhibitor for a coenzyme in the alcohol dehydrogenase reaction.

128

Enzymes and Immunoglobulins COOH I H2

I

:x

~ N~

NH2

H 2

N

N

JCHd~

II: rr

H2

:H-00:

~

N

pterldlne portlOn

FIGURE 4.10.

I

'I '\

:I

-

C,NH-CH :I I COOH

:: I'.- amInobenzoic acId portion

: :I

L-glutamate portion

Structure of methotrexate.

complexed with a zinc atom at the enzyme's active site (McFarland et aI., 1975). Protocatechuate 3, 4-dioxygenase [3, 4-dihydroxybenzoage: oxygen oxidoreductase (decycling)] is a nonheme enzyme catalyzing the cleavage of catechols to cis-cis-muconic acid (see Chapter 11, Section 3.1). Various compounds form enzyme-inhibitor complexes. Resonance Raman spectroscopy indicates that some compounds inhibit enzyme activity by attaching to the active-site iron, whereas others attach to the tyrosine side chain. Thus Raman spectroscopy can be used to identify the site of interactions in enzyme-inhibitor complexes (Que and Epstein, 1981). 2.5.

ENZYME-DRUG INTERACTION

Methotrexate (Figure 4.10) is a drug used for the treatment of childhood leukemia. Dihydrofolate reductase catalyzes the NADPH-linked reduction of dihydrofolate to tetrahydrofolate. Methotrexate inhibits this enzyme. Methotrexate is structurally similar to folate and contains p-aminobenzoyl and pteridine groups, which are both resonance-active chromophores. These groups can be excited at 324 and 350 nm, respectively. By using two different wavelengths for excitation, one can monitor the geometric conformations of both chromophores (Ozaki et aI., 1981). The 1685 cm -1 Raman band can be observed in the NADPH-enzyme binary complex but is absent from the NADPH-methotrexate-enzyme ternary complex. This is ascribed to stabilization of the polarized form of the carboxamide of NADPH by hydrogen bonding to the NH and CO groups of the peptide backbone of dihydrofolate reductase in the ternary complex (Dwivedi et al., 1982). Raman spectra reveal that protonation of the pteridine ring occurs when the drug is bound to the enzyme. At pH 7, there is a strong band at 659 cm- 1 that is present only in the drug-enzyme complex (Saperstein et aI., 1978).

3.

ISOZYMES

Some enzymes have different electrophoretic mobility and different physical properties, although they have the same enzyme activity (isozymes). Acid phosphatase from rat liver has two isozymes, I and II. The two isozymes have

Immunology

129

different Raman spectra in the range 10-1800 cm - I (Twardowsky, 1978), illustrating that some isozymes can be differentiated by Raman spectroscopic technique. The difference in the Raman spectra probably originates from different quantities of carbohydrate attached to the apoenzyme moieties. Sialic acid is a prosthetic group of acid phosphatases. After neuraminidase treatment to hydrolyze neuraminic acid, the low-frequency bands below 300 cm- I disappear, and the difference in Raman spectra for the two isozymes is eliminated (Twardowsky, 1979).

4.

IMMUNOLOGY

Antibodies, or immunoglobulins, are Y-shaped molecules consisting of two heavy and two light polypeptide chains. Several disulfide bonds connect these chains. There are several classes of immunoglobulins, such as IgG, IgA, IgM, IgD, and IgE. An immunoglobulin molecule has both "constant" and" variable" regions and the same class of immunoglobulins contains similar "constant regions." 4.1.

ANTIGEN-ANTIBODY REACTIONS

When antigen (Ag) combines with its antibody (Ab) to form an Ag-Ab complex, it frequently precipitates. Raman study indicates that immunoglobulins are composed predominantly of antiparallel-f3-sheet structure, and they change conformation on binding with an antigen so that the protein becomes more disordered (Painter and Koenig, 1975).

HumanIgG Rabbit IgG Human IgM Ovalbumin-rabbit antiovalbumin precipitate

4.2.

Amide I (cm- I )

Amide III (cm- I )

1673 1673 1673 1673

1238 cm1239 1238 1236 } 1248

I

}

Anti parallelf3-sheet A mixture of f3-sheet and random coil

HAPTEN-ANTIBODY INTERACTIONS

Antigenicity is usually a property of proteins and some polysaccharides. Small molecules are usually not antigenic. However, some small molecules, when attached to a protein, do cause production of antibody that can specifically bind to this small molecule. Such a small compound is called a hapten. The

130

Enzymes and Immunoglobulins

H~9;_", ,Q!NO/'----6\

O

-NiT

o SO; \...

,

- -.- -

I

21

I

,

I

\~02 //

I "l

Serve as a

chromophore for resonance Raman spec-

Serve as an active moiety for hapten

troscopy

FIGURE 4.11. Structure of l-hydroxy(2,4-dinitrophenylazo)-2, 5-napthalenedisulfonic acid. This compound has two active functional groups. One is a resonance-Raman-active chromophore and the other is a hapten-active group.

dinitrophenyl group is a classical example of a hapten. An azo compound is a good chromophore for resonance Raman scattering; therefore, the dinitrophenyl group conjugated with the azo group will serve as an antigen as well as a resonance-Raman-active compound. One example of such a conjugated compound is shown in Figure 4.11. The trans form of the N =N stretching vibration is in the region of 1380-1440 cm- I . When the hapten shown in Figure 4.11 is complexed with its antibody, the PN=N increases, suggesting that the C=M bond of the azo linkage is twisted. The barrier to rotation about the Phe-N bond is larger than 7 kcaljmol. Therefore, quite large amounts of distortion energy are involved (Carey et al., 1973). The IgA protein secreted by the mouse myeloma cell line MOPC 315 has a high affinity for e-DNP-L-lysine and related compounds. Since the DNP group is a chromophore for resonance Raman spectroscopy, the DNP-binding sites of MOPC 315 IgA and of MOPC 460 IgA can be studied. All ligands show significant shifts in their Raman bands, but the shifts are different depending on the source of the antibodies. From this it can be concluded the DNP sites in the two proteins are distinct (Kumar et al., 1978). 4.3.

CRYOGLOBULIN

Monoclonal cryoglobulins decrease in solubility as the temperature of sera is reduced from 37 to O°e. They belong to the immunoglobulin classes IgM, IgG, and IgA. It is important to discover whether a conformational change is involved when they undergo cryoprecipitation. Raman spectral analysis indicates that there is no peptide-backbone structural change over the temperature interval of 40 to - 8°C, during which cryoprecipitation of IgM-K McE occurs. Thus the temperature-dependent solubility may be due to changes in the environment of certain aromatic groups (Middaugh et al., 1977, 1978; Thomas et al., 1979; Scoville et al., 1980).

References

131

REFERENCES Berliner, L. J., and Wong, S. S. (1974). Spin-labeled sulfonyl fluorides as active site probes of protease structure. J. Bioi. Chem. 249, 1668. Campbell, 1. R., Clark, R. J. H., Clore, G. M., and Lane, A N. (1980). Characterization of the electronic properties and geometric environment of the iron atom in the "myoglobin hydrogen-peroxide" complex by Soret-excited resonance Raman spectroscopy. Inorganica Chimica Acta 46,77. Carey, P. R. (1981). Resonance Raman spectroscopic studies of transient enzyme-substrate complexes. Can. J. Spectros., 26, 134. Carey, P. R., and King, R. W. (1979). Neoprontosil binding to carbonic anhydrase. Resonance Raman and other studies on the ionization behavior of the sulfonamide. Biochemistry 18, 2834. Carey, P. R., and Schneider, H. (1974). Resonance Raman spectra of chymotrypsin acyl enzymes. Biochem. Biophys. Res. Commun. 57, 83!. Carey, P. R., and Schneider, H. (1976). Evidence for a structural change in the substrate preceding hydrolysis of a chymotrypsin acyl enzyme: Application of the resonance Raman labelling technique to a dynamic biochemical system. J. Mol. Bioi. 102, 679. Carey, P. R., and Schneider, H. (1978). Resonance Raman labels: A submolecular probe for interactions in biochemical and biological systems. Accts. Chem. Res. 11, 122. Carey, P. R., Schneider, H., and Bernstein, H. 1. (1972). Raman spectroscopic studies of ligand-protein interactions: The binding of methyl orange by bovine serum albumin. Biochem. Biophys. Res. Commun. 47, 588. Carey, P. R., Froese, A, and Schneider, H. (1973). Resonance Raman spectroscopic studies of 2,4-dinitrophenyl hapten-antibody interactions. Biochemistry 12, 2198. Carey, P. R., Carriere, R. G., Lynn, K. R., and Schneider, H. (1976). Resonance Raman evidence for substrate reorganization in the active site of papain. Biochemistry 15, 2387. Carey, P. R., Carriere, R. G., Phelps, D. 1., and Schneider, H. (1978). Charge effects in the active site of papain: Resonance Raman and absorption evidence for electron polarization occurring in the acyl group of some acylpapains. Biochemistry 17, 108!. Dupaix, A, Bechet, J.-J., Yon, 1., Merlin, J.-c., Delhaye, M., and Hill, M. (1975). Resonance Raman spectroscopic studies of the interactions between trypsin and a competitive inhibitor. Proc. Nat. Acad. Sci. 72, 4223. Dwivedi, C. M., Plante, L. T., Kisliuk, R. L., Pastore, E. J., Verma, S. P., and Wallach, D. F. H. (1982). Interaction of the carboxamide of NADPH with Lactobacillus casei dihydrofolate reductase. Arch. Biochem. Biohpys. 213, 338. Evelhoch, J. L., Bocian, D. F., and Sudmeier, J. L. (1981). Evidence for direct metal-nitrogen binding in aromatic sulfonamide complexes of cadmium(II)-substituted carbonic anhydrases by cadmium-I 13 nuclear magnetic resonance. Biochemistry 20, 495!. Hess, G. P., and Seybert, D. (1975). Tetrahedral intermediate in a specific a-chymotrypsin inhibitor complex detected by laser Raman spectroscopy. Science 189, 384. Jagodzinski, P. W., and Peticolas, W. L. (1981). Resonance enhanced Raman identification of the zinc-oxygen bond in a horse liver alcohol dehydrogenase-nicotinamide adenine dinucleotidealdehyde transient chemical intermediate. J. Am. Chem. Soc. 103, 234. Kim, B.-K (1975). Interaction of methylorange with some proteins and cationic surfactants. Seoul. Univ. Faculty Papers 4, 75. Kim, B.-K, Kagayama, A, Saito, Y, Machida, K, and Uno, T. (1975). Resonance Raman spectra of methylorange bound to proteins and cationic surfactants. Bull. Chem. Soc. Japan 48, 1394. Krieger, M., Kay, L. M., and Stroud, R. M. (1974). Structure and specific binding of trypsin: Comparison of inhibited derivatives and a model for substrate binding. J. Mol. Bioi. 83, 209.

132

Enzymes and Immunoglobulins

Kumar, K, King, R. W., and Carey, P. R. (1974). Carbonic anhydrase-aromatic sulfonamide complexes, a resonance Raman study. FEBS Lett. 48, 283. Kumar, K, King, R. W., and Carey, P. R. (1976). Resonance Raman studies on some carbonic anhydrase-aromatic sulfonamide complexes. Biochemistry 15, 2195. Kumar, K, Phelps, D. J., Carey, P. R., and Young, N. M. (1978). Resonance Raman spectroscopic studies of the hapten features involved in the binding of 2,4-dinitrophenyl haptens by the mouse myeloma proteins MOPC 315 and MOPC 460. Biochem. J. 175, 727. Li, T-Y., Chen, J. F., Watters, K 1., and McFarland, J. T (1979). Identification of enzyme coupling sites with aromatic diazonium salts-a resonance Raman study. Arch. Biochem. Biophys. 197, 477. Liljas, A, Kannan, K K, Bergsten, P.-C., Waara, I., larupp, 1., Lovgren, S., Petef, M. (1972). Crystal structure of human carbonic anhydrase C. Nature, New BioI. 235, 131. Lorriaux, J. 1., Merlin, 1. c., Dupaix, A, and Thomas, E. W. (1979). Spectres Raman de Resonance de derives parasubstitutes de I'Azobenzene. J. Raman Spectrosc. 8, 81. MacClement, B. A E., Carriere, R. G., Phelps, D. J., and Carey, P. R. (1981). Evidence for two acyl group conformations in some furylacryloyl and thienylacryloy1chymotrypsin: Resonance Raman studies of enzyme-substrate intermediates at pH 3.0. Biochemistry 20, 3438. Masetti, G., Dellepiane, G., and Zerbi, G. (1976). Resonance Raman spectra of azoaldolase and model molecules. In Proc. Int. Conf. Raman Spectrosc. 5th, E. D. Schmid, J. Brandmueller, and W. Kiefer, Eds. Hans Ferdinand Schulz Verlag: Freiburg/Br., Germany, pp. 230-1. McFarland, J. T, Watters, K 1., and Petersen, R. 1. (1975). Resonance Raman investigation of an enzyme-inhibitor complex. Biochemistry 14, 624. Merlin, 1. c., and Thomas, E. W. (1979). Resonance Raman spectroscopic studies of 2-(4'-hydroxyphenylazo)-benzoic acid and some substituted analogs-I. pH effect on spectra. Spectrochimica Acta 35A, 1243. Middaugh, C. R., Thomas, Jr., G. 1., Prescott, B., Aberlin, M. E., and Litman, G. W. (1977). Investigations of the molecular basis for the temperature-dependent insolubility of cryoglobulins. II. Spectroscopic studies of the IgM monoclonal cryoglobulin McE. Biochemistry 16, 2986. Middaugh, C. R., Gerber-Jensen, B., Hurvitz, A, Paluszek, A, Scheffel, c., and Litman, G. W. (1978). Physicochemical characterization of six monoclonal cryoimmunoglobulins: Possible basis for cold-dependent insolubility. Proc. Nat. Acad. Sci. 75, 3440. Ozaki, Y., King, R. W., and Carey, P. R. (1981). Methotrexate and folate binding to dihydrofolate reductase. Separate characterization of the pteridine and p-aminobenzoyl binding sites by resonance Raman spectroscopy. Biochemistry 20, 3219. Painter, P. C., and Koenig, J. 1. (1975). Raman spectroscopic study of the structure of antibodies. Biopolymers 14, 457. Petersen, R. 1., Li, T.-Y., McFarland, J. T., and Watters, K 1. (1977). Determination of ionization state by resonance Raman spectroscopy. Sulfonamide binding to carbonic anhydrase. Biochemistry 16, 726. Phelps, D. J., Schneider, H., and Carey, P. R. (1981). Correlations between reactivity and structure of some chromophoric acy1chymotrypsins by resonance Raman spectroscopy. Biochemistry 20, 3447. Que, 1., and Epstein, R. M. (1981). Resonance Raman studies on protocatechuate 3,4dioxygenaseinhibitor complexes. Biochemistry 20, 2545. Rakshit, G., Spiro, T G., and Uyeda, M. (1976). Resonance Raman evidence for Fe(IV) in compound II of horseradish peroxidase. Biochim. Biophys. Res. Commun. 71, 803. Saperstein, D. D., Rein, A J., Poe, M., and Leahy, M. F. (1978). Binding of methotrexate to Escherichia coli dihydrofolate reductase as measured by visible and ultraviolet resonance Raman spectroscopy. J. Am. Chem. Soc. 100, 4296.

References

133

Scheule, R. K., Van Wart, H. E., Vallee, B. L., and Scheraga, H. A. (1977). Resonance Raman spectroscopy of arsanilazocarboxypeptidase A: Determination of the nature of the azotyrosyl248, zinc complex. Proc. Nat. Acad. Sci. 74, 3273. Scheule, R. K., Van Wart, H. E., Zweifel, B. 0., Vallee, B. L., and Scheraga, H. A. (1979). Resonance Raman spectroscopy of arsanilazocarboxypeptidase A: Assignment of the vibrations of azotyrosyl-248. J. Inorgan. Biochem. 11,283. Scheule, R. K., Van Wart, H. E., Vallee, B. L., and Scheraga, H. A. (1980). Resonance Raman spectroscopy of arsanilazocarboxypeptidase A: Conformational equilibria in solution and crystal phases. Biochemistry 19, 759. Scheule, R. K., Han, S. L., Van Wart, H. E., Vallee, B. L., and Scheraga, H. A. (1981). Resonance Raman spectroscopy of arsanilazocarboxypeptidase A: Mode of inhibitor binding and activesite topography. Biochemistry 20, 1778. Scoville, C. D., Turner, D. H., Lippert, J. L., and Abraham, G. N. (1980). Study of the kinetic and structural properties of a monoclonal immunoglobulin G cryoglobulin. J. BioI. Chern. 255, 5847. Sharma, R. K., Kisliuk, R. L., Verma, S. P., and Wallach, D. F. H. (1975). Study of thymidylate synthetase-function by laser Raman spectroscopy. Biochim. Biophys. Acta 391, 19. Storer, A. c., Murphy, W. F., and Carey, P. R. (1979). The use of resonance Raman spectroscopy to monitor catalytically important bonds during enzymic catalysis. J. BioI. Chern. 254, 3163. Storer, A. c., Phelps, D. J., and Carey, P. R. (1981). Resonance Raman and electronic absorption spectral studies of some ,B-(2-furyl)acryloylglyceraldehyde-3-phosphate dehydrogenases. Biochemistry 20, 3454. Thomas, E. W., and Merlin, 1. C. (1979). Resonance Raman spectroscopic studies of 2-(4'hydroxyphenylazo)-benzoic acid and some substituted analogs - II. Binding to avidin and bovine serum albumin. Spectrochimica Acta 35A, 1251. Thomas, Jr., G. J., Prescott, B., Middaugh, C. R., and Litman, G. W. (1979). Raman spectra and conformational structures of Fabl' and (Fc)51' fragments of cryoglobulin IgM-k McE. Biochim. Biophys. Acta 577, 285. Twardowski, 1. (1978). Laser Raman spectroscopy of acid phosphatase from rat liver. Biopolymers 17, 181. Twardowski, 1. (1979). Laser Raman spectroscopy of acid phosphatase from rat liver after neuraminidase treatment. Biochim. Biophys. Acta 578, 116. Twardowski, 1., and Proniewicz, L. M. (1980). Chemical aspects of the study of the active site of acid phosphatase from rat liver by spectroscopic methods. Zesz. Nauk. Uniw. Jagiellon., Pro Chern. 25, 93. Woodruff, W. H., and Spiro, T. G. (1974). Resonance Raman spectroscopy of reaction intermediates by a rapid mixing, continuous flow technique. Appl. Spectrosc. 28, 576.

CHAPTER

:)

Nucleic Acids

Raman spectroscopy is extensively used for the study of nucleic acid conformation and mechanism of interaction with other compounds. Nucleic acids show many structurally sensitive Raman lines; by using these lines, one can follow the progress of conformational changes or interactions. In nature the majority of nucleic acids occur as nucleoproteins such as ribosomes, chromatins, and viruses. How does a nucleic acid interact with protein? How do some drugs combine with nucleic acids? To answer these questions, Raman spectroscopy is now being utilized more often. With the advances in computer technology, the intensity changes in Raman lines of nucleic acids can be measured more accurately than before. It can be expected that Raman spectroscopy will playa dominant role in such studies in the future. 1.

BACKGROUND

Nucleosides, nucleotides, and polynucleotides are all constituted of purine and pyrimidine bases. One really cannot discuss the Raman spectroscopic properties of bases alone. It is best to discuss some of the properties of purine and pyrimidine bases together with those of nucleosides, nucleotides, and nucleic acids. In this section a few selected topics are discussed.

Background

1.1.

135

TAUTOMERISM

The structures of purine and pyrimidine bases can be written in keto or enol form. An important question is which form guanine, inosine, and cytosine take. Raman spectroscopy solves this problem readily, as these compounds show an intense keto band at 1670 em- I and other characteristic bands associated with the keto group. Therefore, guanine, inosine, and cytosine in nucleosides and nucleotide derivatives exist in the keto form (Lord and Thomas, 1968; Medeiros and Thomas, 1971a). However, the free bases can show tautomerism in solution depending on the dielectric constant of the solvent, the temperature, and the ionic strength of the solution. Detailed Raman analyses of free uracil and thymine have been made to differentiate between tautomers (Lippert, 1979).

1.2.

HYDROGEN-DEUTERIUM EXCHANGE

The hydrogen atom at C-8 of purine in nucleic acid can be exchanged with deuterium. In poly(A), C(8)-H and C(8)-D deformation vibrations appear at 1485 and 1462 cm- I , respectively (Livramento and Thomas, 1974) (Figure 5.1). Using the measurement of intensity changes at 1485 and 1462 cm- 1 at different temperatures, it is possible to measure parameters of hydrogendeuterium-exchange kinetics such as the activation energy and the frequency factor for different nucleotides (Thomas and Livramento, 1975; Lane and Thomas, 1979). Similarly, the C(8)-H of GMP and cyclic GMP can be exchanged with deuterium, and this can also be followed by Raman spectroscopy (Thomas and Lane, 1980). Ringland et al. (1979) attempted to use the slow C-8 exchange to obtain information on the tertiary structure of calf-thymus chromatin. 1.3.

ORIGIN OF BASE VIBRATIONS

Exact assignment of every vibrational band for all nucleosides and nucleotides is not an easy matter. By using deuterium and 15N isotopic substitutions, some assignments can be made. For instance, the Raman spectrum of guanosine can

~N ~.,A>-H N N I

R FIGURE 5.1.

N0

°2° H0 2

6:>-0 2

I

R

Hydrogen-deuterium exchange in adenine.

136

Nucleic Acids Purine ring

'"

r·

~

1--

ribose

Vibrational modes of different parts of guanosine.

be traced to C=O stretching, overall ring vibration, the pyrimidine part of the purine ring, the imidazole part of the purine ring, and ribose (Figure 5.2). Oelabar and Guschlbauer (1979) assigned the guanosine vibrations as follows: Pyrimidine-portion vibrations Purine-ring vibrations Ribose-ring vibrations

1605 and 1577 cm- I at 60°C and 1585 cm- I at 10°C 1540, 1323, 1180, and 650 cm -I at 60°C and 1540,1325,1182, and 650 cm- I at 10°C 1080, 1030, and 865 cm - I at 60°C and 1080, 1030, and 870 cm - I at 10°C

The molecular breathing vibration usually appears at lower frequency. The 651 cm- I band of guanine is assigned to the ring-breathing vibration (Majoube, 1978). Some bases such as uracil, guanine, cytosine, and hypoxanthine contain carbonyl groups that show bands in the region of 1500-1700 cm -I. The band from the carbonyl group in uracil is much more intense than that from the carbonyl group in guanine and cytosine; thus it dominates the spectra of RNA (Rice and Thomas, 1972). Thymine contains two C=O groups; the one at C-2 shows a band at the highest frequency, and the C(4)=0 shows a band at slightly lower frequency, in the region of 1671-1674 em-I. Similarly, uracil also contains two C=O groups. The C(2)=0 of poly(D) shows a band at the higher frequency of 1695 cm- I , and C(4)=0 shows a band at 1658 cm- I at 25°C in 020. At 5°C in 020' the C(2)=0 band appears at 1698 em-I, and the C(4)=0 gives a doublet at 1675 and 1641 em -I. In water at 25°C, poly (D) gives two C=O bands at 1686 and 1629 em-I (Schmid and Gramlich, 1979). Temperature definitely has an effect on the C=O band. Lower temperatures tend to give better resolution. Examples that show the temperature effect are GpA and ApG. They show the C=O stretching at 1689 cm- 1 at 45°C, whereas at 5°C

137

Principal Raman Lines

the C=O bond exhibits two distinct stretching vibrations at 1725 and 1680 cm - I for both GpA and ApG. This change probably reflects the different states of hydrogen bonding at different temperatures. There are several chemical groups that give C-O stretching vibrations; they often have slightly different frequencies, which can be used to detect different functional groups. The range in keto stretching vibrations of different functional groups is summarized here:

Carboxyl

°II

-C-O-H

°II Carboxylate ion

-C-O-

1660-1740 cm- I asym 1340-1440 cm-

1

asym 1550-1690 cm- I

°II Ester

-C-OR

Amide

-C-NH 2

°II °II

Ketone

C-C-C

°II Aldehyde

H-C-C

1700-1746 cm- I

~

1675 cm- I

1700-1720 cm- I

1710-1740 cm- I

The C=O stretching vibration usually gives a prominent band. The band is quite stable and does not fluctuate in different solvents. For instance, the bands from the NADH nicotinamide C=O stretching vibration in H 2 0, D 2 0, and dimethyl sulfoxide all appear at 1689 cm- I (Patrick et aI., 1974). The primary-amide C=O band is different for NADH and NAD. The latter gives a weaker C=O stretching band at 1698 cm- I (Forrest, 1976).

2.

PRINCIPAL RAMAN LINES

Before we study the properties of nucleic acids and their derivatives or their interaction with other compounds, it is essential to know what each Raman band means. The band assignment, therefore, is important. This section looks into the origin of nucleic acid Raman bands. The next section discusses the Raman bands that are most useful in the study of nucleic acid structures and properties.

138 2.1.

Nucleic Acids

AQUEOUS SOLUTION

There are many structurally sensitive Raman bands in spectra of nucleic acids. Because nucleic acids usually contain at least four different types of bases, the band assignments are more complicated than individual nucleotide. Synthetic polynucleotides are convenient to study because some contain only one base. Before going over the structurally sensitive bands of nucleic acids, it is best to summarize the Raman bands and their assignment for synthetic polynucleotides in aqueous solution. The detailed assignments of the bands in spectra of poly(G), poly(A), poly(l), poly(C), and poly(U) are shown in Table 5.1. In the detailed band assignment of dA and dT, it is shown that the bands in the region from 1240 to 1700 cm - I are exclusively due to base vibrations, and bands in the 1000-1240 cm - I region are due to the backbone con tribu tions. For instance, a PO; antisymmetrical stretching vibration appears at 1240 cm - I, and a PO; symmetrical stretching vibration appears at 1100 cm - '. Some deoxyribose vibrations also appear in this region (Baret et a1., 1979). TABLE 5.1.

Assignment of Raman Frequencies of Synthetic Polynucleotides

Poly(A)

Poly(G)

Poly(l)

Poly(C)

Poly(U)

(em-I)

(em-I)

(em-I)

(em-I)

(em-')

Vibrations of Bases

705 725 1228 1252 1303 1336 1337 1424 1483 1508 1576

675 691 722 782 1207 1242 1267 1326 1330 1360 1367 1390 1419 1483-1485 1535-1543 1583-1585

723 1269 1323 1352 1384 1422 1518 1556 1594

750 783-784 790 991 1194 1248-1256 1290-1292 1365 1384 1408-1410 1527 1547

783 . 1233 1399 1476

Ribose

1466

1135 1470

1464

1144 1466

810

800

1097-109R

1094

Phosphate Diester Symmetric Stretch

811

819-820

794 (disordered)

Ionic (O-P-O) Symmetric Stretch IOQ'\

IOR7-IOQ6

10QI

i

IlTABLE 5.1. ·h"

Poly(A) (em-I)

'IJ ,,','

,Ie

Continued Poly(G) (em-I)

Poly(I) (em-I)

Poly(C) (em-I)

Poly(U) (em-I)

/.'

..

1/

Ribose-Phosphate

533 635 868 912

408 429 505 588 640 975

529 559 822 912 969 1158

429 545 596 601 625

556 639 997

644

710 760 845 866 915-916 975 1008 1047 Base External C-N Stretch

il79

1183

1042

915 (C-O and C-N) 1025-1026 1046 1070 (C-O and C-N)

1180 C-O Stretch

1050

1042

C-C and C-N Stretch

1100 1175 1220 1245 C-H Deformation

1465

1462 C=O Stretch

1608 1680

1680

Source: The table was constructed based on the papers of Petico1as (1971), Rice et al. () 973) and Chou and Thomas (1977).

TABLE 5.2.

Poly(rA)

360(0) 530(0) 560(0) 585(0)

643(1) 700(S) 716(5) 760(0) 810(4) 855(1) 870(0) 912(0) 985(0) 1043(0) 1094(3) 1185(4)

Raman Frequencies of POly(A), Poly(C), and Poly(U) In 0 20

Poly(rC) 275(0) 310(0) 362(1) 425(0) 547(0) 600(1) 613(S) 650(0) 705(0) 750(2) 775(10) 810(4) 840(0) 870(0) 910(0) 982(0) 1035(1) 1088(S) 1098(2) 1132(0) 1175(4) I 190(?)

1218(S) 1260(0) 1303(7) 1341(10) 1380(2)

1253(8) 1293(7) 1325(0) 1375(0)

1425(0) I463(S) 1480(5) 1520(1) 1550(0) 1572(5) 1623(0)

1415(0) 1462(1) 1503(3) 1520(2)

1618(3) 1650(2)

Poly(rU)

415(0) 550(2) 570(S) 620(1) 637(S) 710(0)

778(10) 797(4) 865(0) 915(0) 975(0) 1045(0) 1094(2) 1136(3) 1190(?) 1217(7) 1237(S) 1252(10) 1300(5) I380(S) 1400(3) 1422(0) I462( I)

1620(2) 1662(10) 1695(6)

Assignment a Ring Ring Ring Ring Ring Ribose Ribose Ribose Ribose Ribose Ribose Ring Ribose Ring OPO sym. str. Ribose-phosphate Ribose Ribose Ribose Ribose Ring P0 2 sym. str. Ring Ring Ring Ring Ring Ring Ring Ring Ring Ring Ring CH def. Ring Ring Ring Ring Ring C=O str. C=O str.

Source: The table was reproduced from Prescott et al. (1974). "Abbreviations: sym., symmetrical; str., stretching; def., deformation; s, shoulder. Numbers in parenthesis give relative line intensities on 0 to 10 scale.

Structurally Sensitive Lines

141

-;

.' 3.

STRUCTURALLY SENSITIVE LINES

There are many structurally sensitive Raman lines for different nucleotides and nucleic acids. Some originate from the vibrations associated with particular bases; some are associated with the sugar-phosphate-backbone bond (815-cm - I line). We will discuss the Raman bands that are useful in nucleic acid research.

3.1.

HEAT TREATMENT

Heating is one good way to alter the structure of nucleic acids. Structural changes of polynucleotides can be followed by measuring the intensity changes of some base vibrational bands. Raman lines sensitive to heat treatment are summarized in Table 5.3. Structurally sensitive lines are not restricted to nucleic acids and their components, but can also be found in spectra of special nucleotides. In NAD and NADH, the 1400-cm- 1 band is assigned to the nicotinamide-ring vibration, which is also sensitive to conformational changes (Barrett, 1980).

3.2.

PH TREATMENT

Some Raman lines are sensitive to pH. These lines are usually associated with functional groups or atoms involved in hydrogen bonding, or the atoms may be protonated or deprotonated. These lines are summarized in Table 5.4.

3.3.

PHOSPHODIESTER-BOND VIBRATIONS

There are two types of phosphodiester-stretching vibrations. One is the phosphodiester-stretching vibration and another is the phosphoionic bond-stretch-

TABLE 5.3.

Compound Uracil Cytosine Guanine

CMP-5'

Inosine, IMP

Poly(C)

Poly(A)

Poly(I) Poly(U)

Structurally Sensitive Raman Lines (Heat Treatment) Raman Line (em-I)

Assignment

785 1235 780 1280 670 1485 1580 783 1243 1530 723 820 1350 1382 1518 1554 1594 790

Base stacking O-P-O Base stacking Base stacking Base stacking Base stacking Base stacking Ring mode

1256

Ring mode

1547

Double-bond stretch

720 725

Base stacking Ring mode

1303

Ring mode

1380 1508 1520 722 790 1236 1240 1660

Ring mode Double-bond stretch Double-bond stretch Ring mode

Reference Arie et aI. (1971) Arie et aI. (1971) Arie et aI. (1971) Arie et aI. (1971) Arie et aI. (1971) Arie et aI. (1971) Arie et aI. (1971) Lord and Thomas (I 967a, b) Lord and Thomas (1967a, b) Lord and Thomas (1967a, b) Medeiros and Thomas (l97Ib) Medeiros and Thomas (1971 b) Medeiros and Thomas (1971 b) Medeiros and Thomas (1971 b) Medeiros and Thomas (1971 b) Medeiros and Thomas (1971 b) Medeiros and Thomas (1 971 b) Small and Peticolas (1971 a) Peticolas (1975) SmaIl and Peticolas (1971 a) Peticolas (1975) Small and Peticolas (1971 a) Peticolas (1975) Tomlinson and Peticolas (1970) Small and Peticolas (1971 a) Peticolas (1975) SmaIl and Peticolas (1971 a) Peticolas (1975) Small and Peticolas (1971 a) Small and Peticolas (1971 a) Peticolas (1975) SmaIl and Peticolas (1971 a) Peticolas (1975) SmaIl and Peticolas (1971 a) Peticolas (1975) SmaIl and Peticolas (1971 a)

,

;..:~,;;­

.~i:

I~'~":

;~:fTABLE

i,I\f_'

5.4.

~n\l'

••~ fe-SlabUe

Tang.1 a!. (1975)

451 509

S-S S-S

Janz el a!. (1976) Nicki... (1968)

/

FC'-ScYt

Fe-SlAbU.

F.S Na.S. H,S,

"This table was reproduced from Freier et aI. (1979).

TABLE 11.3. Typical Metal- Ligand Vibrational Frequencies for Divalent and Trivalent Metal Ions and Various Ligands

Type of Binding

Ligand

Carboxylate

°II

Range of p(M - L), cm- 1 Fe(II)

M-O-C-

350-530

M-O~C_ M-O.;7

400-560

Phenolate

M - O - @ -545-560

Aqua

M-OH 2

Hydroxo (methemoglobin)

M-OH

310-405

Fe(III)

References

McConnell and Nuttall (1977)

Percy and Stenton (1976) 490-540

Adams (1968)

497

Asher et al. (1977)

500-580

Asher et al. (1977)

363 (sym.) 538 (sym.)

Burke et al. (1978) Hewkin & Griffith (1966)

503

Dunn et al. (1973)

H Hydroxobridged p.-Oxobridged

M

/0"

480-560 M

M-O--M M

/,0"

M

Peroxo (oxyhemerythrin)

M-O-O

Superoxo (oxyhemoglobin)

M-O-O

Amine

M-NH 2

Histidine (oxyhemocyanin)

A

M-ioi

Histidine (azurin) Cysteinato (azurin) Cysteinato (Fe-S proteins) -

M-S

300-440

570

Brunner (1974)

510-590

Adams (1968) Nakamoto (1978)

265-285

Freedman et al. (1976)

400-425

Thamann (1980)

369

Thamann (1980)

300-400

Spiro and Loehr (1975)

Source: The table was reproduced from Sjoberg et aI. (1980).

311

312

Nonheme Iron Compounds

s. OTHERS Ribonucleotide reductase converts ribonucleotides to their corresponding deoxyribonucleotides. It has been isolated from E. coli and consists of two nonidentical subunits, proteins Bland B2; the subunit itself has no enzymatic activity. Protein B2 contains two iron atoms per mole of enzyme and at least one tyrosyl free radical that is essential for the enzymatic activity. The iron center in the native B2 protein consists of an antiferromagnetically coupled pair of high-spin Fe(III) atoms. In this respect it is similar to the iron center of hemerythrin. With a chelating agent, the iron atoms can be removed from protein B2, resulting in the disappearance of the radical. Thus B2 becomes an iron-, and radical-free apoprotein B2. Both the native (no tyrosyl radical) and the radical-free enzyme exhibit a resonance-enhanced Raman band at 496 em -I, which is assigned to the Fe-O vibrational mode. This is evidenced by the isotopic shift from 496 em-I to 481 em-I when the enzyme is suspended in H 2 18 0 converting FeO to Fe 180. Since there are no tyrosinate-ring modes, the possibility of tyrosinate oxygen as a ligand is ruled out. By comparison with Fe model compounds, it was concluded that a carboxylate from either an aspartic or glutamic acid residue or an oxygen-containing group from the solvent, such as H 20, OH- , or a p.-oxo bridge (similar to the iron center in hemerythrin), is a ligand (Table 11.3) (Sjoberg et al., 1980, 1982). Nitrogenase from Azotobacter vinelandii contains not only iron but also molybdenum, sulfur, and coenzyme A. It is important to know its structure and function in order to understand the mechanism of biological nitrogen fixation. As a first step toward this goal Fe, Mo-cofactors, which may be involved in the nitrogenase active site, were investigated by Raman spectroscopy. The Fe-S stretching vibrational band can be observed at 368 em-I. There are also intensive bands at 1600 and 1400 em-I, which are asymmetrical and symmetrical stretching vibrations of the carboxylate ion (-COO-). The result is interpreted as the presence of coenzyme A as a component of the Fe, Mo-cofactors of nitrogenase (Levchenko et al., 1980).

REFERENCES Adams, D. M. (1968). Metal-Ligand and Related Vibrations, St. Martin's Press, New York. Adar, F., Blum, R., Leigh, Jr., J. S., Ohnishi, T., and Salerno, J. (1977). Anti-ferromagnetic exchange in beef adrenodoxin as measured by resonance Raman spectroscopy. FEBS Lett. 84, 214. Ainscough, E. W., Brodie, A. M., Plowman, 1. E., Bloor, S. 1., Loehr, J. S., and Loehr, T. M. (1980). Studies on human lactoferrin by electron paramagnetic resonance, fluorescence, and resonance Raman spectroscopy. Biochemistry 19, 4072. Aisen, P., and Listowsky, 1. (1980). Iron transport and storage proteins. Ann. Rev. Biochem. 49,

357.

.

j

References

313

Asher, S. A, Vickery, L. E., Schuster, T. M., and Sauer, K. (1977). Resonance Raman spectra of methemoglobin derivatives. Selective enhancement of axial ligand vibration and lack of an effect of inositol hexaphosphate. Biochemistry 16, 5849. Averill, B. A, and Orme-Johnson, W. H. (1978). Iron-sulfur proteins and their analogs. In Metal Ions in Biological Systems, H. Sigel, Ed., Dekker, New York, pp. 127-183. Bain, 0., and Giguere, P. A (1955). Hydrogen peroxide and its analogues. VI. Infrared spectra of HzO z , DzO z , and HD01. Can. 1. Chem. 33,527. Barlow, C. H., Maxwell, J. c., Wallace, W. J., and Caughey, W. S. (1973). Elucidation of the mode of binding of oxygen to iron in oxyhemoglobin by infrared spectroscopy. Biochem. Biophys. Res. Commun. 55, 91. Blum, H., Adar, F., Salerno, J. C., and Leigh, Jr., J. S. (1977). Exchange coupling in spinach ferredoxin determined by resonance Raman spectroscopy Biochem. Biophys. Res. Commun. 77,650. Brunner, H. (1974). Identification of the iron-ligand vibration of oxyhemoglobin. NatUlwissenscha/ten 61, 129. Bull,

c., Ballou, D. P., Salmeen, I. (1979). Raman spectrum of protocatechuate dioxygenase from Pseudomonas putida; new low frequency bands. Biochem. Biophys. Res. Commun. 87, 836.

Burke, J. M., Kincaid, J. R., Peters, S. Gagne, R. R., Collman, J. P., and Spiro, T. G. (1978). Structure-sensitive resonance Raman bands of tetraphenyl and "picket fence" porphyrin-iron complexes, including an oxyhemoglobin analogue. 1. Am. Chem. Soc. 100,6083. Carey, P. R., and Young, N. M. (1974). The resonance Raman spectrum of the metalloprotein ovotransferrin. Can. J. Biochem. 52, 273. Duff, L. L., Klippenstein, G. L., Shriver, D. F., and Klotz, I. M. (1981). Multiple conformations at functional site of hemerythrin: Evidence from resonance Raman spectra. Proc. Nat. A cad. Sci. USA 78,4138. Dunn, J. B. R., Shriver, D. F., and Klotz, I. M. (1973). Resonance Raman studies of the electronic state of oxygen in hemerythrin. Proc. Nat. A cad. Sci. 79, 2582. Dunn, J. B. R., Shriver, D. F., and Klotz, I. M. (1975). Resonance Raman studies of hemerythrinligand complexes. Biochemistry 14, 2689. Dunn, J. B. R., Addison, A W., Bruce, R. E., Loehr, J. S., and Loehr, T. M. (1977). Comparison of hemerythrins from four species of sipunculids by optical absorption, circular dichroism, nuorescence emission, and resonance Raman spectroscopy. Biochemistry 16, 1743. Felton, R. H., Cheung, L. D., Phillips, R. S., and May, S. W. (1978). A resonance Raman study of substrate and inhibitor binding to protocatechuate-3,4-dioxygenase. Biochem. Biophys. Res. Commull. 85, 844. Freedman, T. B., Loehr, J. S., and Loehr, T. M. (1976). A resonance Raman study of the copper protein, hemocyanin. New evidence for the structure of the oxygen-binding site. J. Am. Chern. Soc. 98, 2809. Freier, S. M., Duff, L. L., Van Duyne, R. P., and Klotz, I. M. (1979). Resonance Raman studies and structure of a sulfide complex of methemerythrin. Biochemistry 24, 5372. Freier, S. M., Duff, L. L., Shriver, D. F., and Klotz, 1. M. (1980). Resonance Raman spectroscopy of iron-oxygen vibrations in hemerythrin. Arch. Biochem. Biophys. 205,449. Gaber, B. P., Miskowski, V., and Spiro, T. G. (1974). Resonance Raman scattering from iron(III)and copper(II)-transferrin and an iron(III) model compound. A spectroscopic interpretation of the transferrin binding site. J. Am. Chern. Soc. 96, 6868. Gaber, B. P., Sheridan, J. P., and Roberts, R. M. (1978). Raman scattering from progesteroneinduced glycoprotein. In Proc. Sixth Jill. Conf. Raman Spectrosc., E. D. Schmid, R. S. Krishnan, W. Kiefer, and H. W. Schrotter, Eds., Heyden, London, Philadelphia, Rheine, pp. 112-113.

314

Nonheme Iron Compounds

Gaber, B. P., Sheridan, J P., Bazer, F. W., and Roberts, R. M. (1979). Resonance Raman scattering from uteroferrin, the purple glycoprotein of the porcine uterus. J. BioI. Chem. 254, 8340. Hawkin, D. J, and Griffith, W. P. (1966). Infrared spectra of binuclear complexes. J. Chem. Soc. (A), 472. Herzberg, G. (1945). Infrared and Raman Spectra of Polyatomic Molecules. Van Nostrand, New York. Janz, G. J, Roduner, E., Coutts, J. W., and Downey, Jr., J R. (1976). Raman studies of sulfur-containing anions in inorganic polysulfides. Barium trisulfide.lnorg. Chem. IS, 1751. Johnson, M. K., Hare, J. W., Spiro, T. S., Moura, J J G., Xavier, A V., and LeGall, J (1981). Resonance Raman spectra of three-iron centers in ferredoxins from Desulfovibrio gigas. J. Bioi. Chem. 256, 9806. Keyes, W. E., and Loehr, T. M. (1978). Raman spectral evidence for tyrosine coordination of iron in protocatechuate 3,4-dioxygenase. Biochem. Biophys. Res. Comm. 83, 941. Keyes, W. E., Loehr, T. M., Taylor, M. L., and Loehr, J. S. (1979). Protocatechuate 3,4dioxygenase. Resonance Raman studies of the oxygenated intermediatc. Biochem. Biophys. Res. Comm. 89,420. Klotz, 1. M., Klippenstein, G. L., and Hendrickson, W. A (1976). Hemerythrin: Alternative oxygen carrier. Science 192, 335. Kurtz, Jr., D. M. (1977). Structural investigations of the active sites of hemcrythrin and hemocyanin by isotopic vibrational analyses of resonance Raman spectra. Diss. Abstr. Till. B, 38(9), 4205. Kurtz, D. M., Shriver, D. F., and Klotz, I. M. (1976). Resonance Raman spectroscopy with unsymmetrically isotopic ligands. Differentiation of possible structure of hemerythrin complexes. J. Am. Chem. Soc. 98, 5033. Levchenko, L. A, Roschupkina, O. S., Sadkov, A P., Marakushev, S. A, Mikhailov, G. M., and Borod'ko, Yu. G. (1980). Spectroscopic investigation of FeMo-Cofactor. Coenzyme A as one of the probable components of an active site of nitrogenase. Biochem. Biophys. Res. Commun. 96, 1384. Loehr, J S., Freedman, T. B., and Loehr, T. M. (1974). Oxygen binding to hemocyanin: A resonance Raman spectroscopic study. Biochem. Biophys. Res. Commun. 56, 510. Long, II, T. V., and Loehr, T. M. (1970). The possible determination of iron coordination in nonheme iron proteins using laser-Raman spectroscopy. Rubredoxin. J. Am. Chem. Soc. 92, 6384. Long, II, T. V., Loehr, T. M., Allkins, JR., and Lovenberg, W. (1971). Determination of iron coordination in nonheme iron proteins using laser-Raman spectroscopy. II. Clostridium pasteurianum rubredoxin in aqueous solution. J. Am. Chern. Soc. 93, 1809. Lovenberg, W. (1973). Iron-Sulfur Proteins, Vol. II, Molecular Biology Series, Academic, New York. May, S. W., and Kuo, J-Y. (1978). Preparation and properties of cobalt (II) rubredoxin. Biochemistry 17, 3333. McConnell, A A, and Nuttall, R. H. (1977). The vibrational spectra of EDTA complexes of divalent tin and lead. Spectrochim. Acta 33A, 459. Milligan, D. E., and Jacox, M. E. (1963). Infrared spectroscopic evidence for the species H0 2 . J. Chem. Phys. 38, 2627. Nakamoto, K. (1978). Infrared and Raman Spectra of Inorganic and Coordination Compounds, 3rd ed., Wiley, New York. Nickless, G. (1968). Inorganic Sulfur Chemistry, Elsevier, Amsterdam. Percy, G. c., and Stenton, H. S. (1976). Infrared and electronic spectra of N-salicylideneglycinate complexes of cobalt and nickel. Spectrochim. Acta 32A, 1615. .J

References

315

Que, Jr., L., and Epstein, R. M. (1981). Resonance Raman studies on protocatechuate 3,4dioxygenase-inhibitor complexes. Biochemistry 20, 2545. Que, Jr., L., and Heistand, II, R. H. (1979). Resonance Raman studies on pyrocatechase. J. Am. Chern. Soc. 101, 2219. Que, Jr., L., Heistand, II, R. H., Mayer, R., and Roe, A. L. (1980). Resonance Raman studies of pyrocatechase-inhibitor complexes. Biochemistry 19, 2588. Scovell, W. M., and Spiro, T. G. (1974). Vibrational and Raman intensity analysis of a ferredoxin model: S2Fe2(COk Inorg. Chern. 13,304. Sjoberg, E.-M., Graslund, A., Loehr, 1. S., and Loehr, T. M. (1980). Ribonucleotide reductase: A structural study of the dimeric iron site. Biochem. Biophys. Res. Commun. 94, 793. Sjoberg, B.-M., Loehr, T. M., and Sanders-Loehr, 1. (1982). Raman spectral evidence for a p.-oxo bridge in the binuclear iron center of ribonucleotide reductase. Biochemistry 21, 96. Spiro, T. G., and Loehr, T. M. (1975). Resonance Raman spectra of heme proteins and other biological systems. In Advances in Infrared and Raman Spectroscopy, Vol. I, R. 1. H. Clark and R. E. Hester, Eds., Heyden, London, New York, Rheine, pp. 98-142. Sweeney, W. V., and Rabinowitz, 1. C. (1980). Proteins containing 4Fe-4S clusters: An overview. Ann. Rev. Biochem. 49, 139. Tang, S.-P. W., Spiro. T. G., Mukai, K., and Kimura, T. (1973). Resonance Raman scattering and optical absorption or adrenodoxin and selenaadrenodoxin. Biochem. Biophys. Res. Commun. 53,869. Tang, S.-P. W., Spiro, T. G., Antanaitis, c., Moss, T. H., Holm, R. H., Herskovitz, T., and Mortensen, L. E. (1975). Resonance Raman spectroscopic evidence for structural variation among bacterial ferredoxin, Hi PIP, and Fe4S4(SCH2Ph)~- . Biochem. Biophys. Res. Commun. 62, I. Tatsuno, Y., Saeki, Y., IWaki, M., Yagi, T., Nozaki, M. (1978). Resonance Raman spectra of protocatechuate 3, 4-dioxygenase. Evidence for coordination of tyrosine residue to ferric iron. J. Am. Chern. Soc. 100,4614. Thamann, T. 1. (1979). Structural investigations of the active sites of azurin, hemerythrin, and hemocyanin, and vibrational analyses of the copper(II) and copper(III) complexes of biuret and oxamide. Diss. Abstr. Int. 41, No. 8109791. Tomimatsu, Y., Kint, S., and Scherer, J. R. (1973). Resonance Raman spectroscopy of iron(III)ovotransferrin. Biochem. Biophys. Res. Commun. 54, 1067. Tomimatsu, Y., Kint, S., and Scherer, 1. R. (1976). Resonance Raman spectra of iron(III)-, copper(II)-, cobalt(lII)-, and manganese(III)-transferrins and of bis(2, 4, 6trichlorophenoJato)diimidazolecopper(II) monohydrate, a possible model for copper(II) binding to transferrins. Biochemistry 15, 4918. Van KreeJ, B. K., van Eijk, H. G., Leijnse, B., and van der Maas, 1. H. (1972). Laser-Raman spectroscopy of the iron-transferrin-bicarbonate complex. Z. Klin. Chern. Klill. Biochem. 10, 566.

CHAPTER

2

Hemes and Porphyrins

The heme of heme proteins can be studied by resonance Raman spectroscopy without interference from scattering by the protein because the intense heme optical absorptions strongly enhance the scattering by heme vibrations. By careful analyses of empirical results, it is sometimes possible to predict the oxidation and spin states of heme iron and the type of axial ligands. It may also be possible to study certain peripheral substituents, as for example, the carbonyl at position 8 in heme a of cytochrome oxidase. This is possible because effects on the chromophore can be reflected in the optical absorption spectra as well as in the resonance Raman spectra. The resonance Raman spectra are due primarily to porphyrin vibrations. However, both oxidation and spin states, as well as quarternary structure and ligand, have indirect effects on the porphyrin. Oxidation and spin states, for example, are properties of the iron atom and not of the porphyrin. There are many good review articles on resonance Raman spectroscopy of heme compounds; readers are advised to see Spiro and Stein (1977), Yu (1977), Kitagawa et al. (1978), and Spiro (1978) for further information.

Vibrational Modes

1.

317

VIBRATIONAL MODES

Heme compounds have two distinct electronic transitions, giving rise to bands in the absorption spectrum near 400 nm (Soret band) and around 500-550 nm (a- and ,B-bands) (Figure 12.1). Resonance-enhanced Raman scattering is observed from the vibrational modes that couple to these electronic transitions. The Raman lines vary in relative intensities depending on the wavelength of laser excitation. The frequency of a vibrational mode cannot change with the excitation. But sometimes two modes with nearly the same frequency may be enhanced differently with different excitations, causing an apparent shift in frequency of an observed band. Raman spectra of heme compounds differ depending on whether they are excited at the Soret or a-band wavelengths (Salmeen et aI., 1973; Spiro and Strekas, 1974). Since the Raman spectra of heme compounds are due to the vibrations of heme rather than those of the protein, heme compounds with identical hemes usually give similar spectra (Strekas and Spiro, 1972a, b; Brunner, 1973; Loehr and Loehr, 1973). Hemeundecapeptide can be obtained from cytochrome c by proteolytic digestion. The Raman spectrum of the hemeundecapeptide is very similar to that of cytochrome c. Raman spectra of many b-type cytochromes

Sorel

,-. , ,, I I I I I I

,,

,, ,, ,

,

I

,,

~ ,.\

I

I~ " '~'''''' '

'

ft

\

400

\._------450

I

I

\

\

"' ...., - , '_ _\

500

550

'

~

_

600

Wavelength (nm)

FIGURE 12.1. Typical absorption spectrum of ----ferrous (reduced) and forms of heme proteins.

ferric (oxidized)

318

Hemes and Porphyrins

are very similar to each other (Adar and Erecinska, 1974; Bullock and Myer, 1978). Using the characteristic Raman lines, b-type can be differentiated from c-type cytochrome (Kitagawa et al., 1975a). For a mixed heme complex such as succinate-cytochrome c reductase, which contains both b- and c-type cytochromes, both hemes contribute to the resonance Raman spectrum. Because of differences in the absorption spectra of the two types of cytochromes, Raman spectra of the reductase depend on the excitation wavelength. At 514.5-nm excitation, the spectrum of reduced succinate-cytochrome c reductase is due to the spectrum of both b- and c-types of cytochromes. The spectrum obtained using light at 568.2 nm is due mostly to b-type cytochrome because of the proximity of the excitation wavelength to its a-absorption band (Adar and Erecinska, 1974). A similar example is found with cytochrome oxidase, which contains both cytochromes a and a 3 • With proper control of the excitation wavelength, two independent hemes can be distinguished by resonance Raman spectroscopy (Woodruff et aJ., 1981). For oxidized cytochrome oxidase, excitation at 441.6 nm enhances the vibrations of only cytochrome a, whereas excitation at 413.1 and 406.7 nm enhances both low-frequency vibrations of cytochrome a 3 and high-frequency vibrations of a and a 3 (Babcock and Salmeen, 1979; Ondrias and Babcock, 1980). Each heme compound has its own characteristic Raman lines. In mixed hemes sometimes these characteristic lines deviate from the line positions of an individual heme. Such deviation can sometimes be interpreted as heme-heme i3teraction (Adar et al., 1981).

1.1.

EXCITATION PROFILES

One way to study heme compounds by Raman spectroscopy is to measure the intensity of Raman scattering as a function of the excitation frequency. When the wavelength of the laser used to excite the Raman spectrum is near an electronic transition of the molecule, an enormous enhancement of the scattered light is observed (see Chapter 1, see Section 5). This enhancement is due to cancellation of terms in the denominator of the first term in equation 5.1 in Chapter 1 when the laser is tuned through the energy of the electronic transition. In general, a number of peaks in the Raman spectrum will result, since the electronic absorption band is made up of many overlapping vibrational-electronic (vibronic) transitions. That is, the vibrational structure of the electronic transition complicates the absorption band. Resonance with these overlapping vibronic levels gives rise to a complicated dependence of the intensity of a Raman line on a wavelength of the laser light used to excite the spectrum. A plot of the intensity of a Raman line versus the exciting light frequency is called an excitation profile. Improved excitation profiles can now be obtained as continuous-range wavelengths of lasers are becoming more available. Excitation profiles are also called Raman dispersion. Each of the Raman lines has an excitation profile.

,.

~:,:

Vibrational Modes

319

A great deal of detailed information about the excited states of heme can be learned from the excitation profiles of its absorption bands. For example, the vibrational frequencies in the ground and excited electronic states may differ. The Raman spectrum gives the vibrational frequencies of the ground electronic state. In contrast, the vibrational frequencies in an excited electronic state may be obtained from the peak positions in the excitations profiles of that electronic state. Thus the vibrational frequencies of heme after absorbing light into the a-band can be determined from the excitation profiles of the a, ,B-band region by measuring the separation of the two peaks in the excitation profile of each Raman line. This procedure has shown the vibrational frequencies to differ only slightly from the ground-state frequencies. Information about the interaction between the electronic and vibrational motion (vibronic coupling) can also be learned from the excitation profiles. For example, quantitative calculations from Raman excitation profiles show that the strength of the vibronic coupling can be quite different for different porphyrins (Cheung et aI., 1978; Shelnutt and O'Shea, 1978, 1980; Shelnutt et al., 1977). Such calculations can also separate the contributions to the Raman intensity from several possible vibronic-coupling mechanisms. For example, intensity in a Raman line can arise from a single electronic state or from vibrational coupling of electronic states of different energies. In metalloporphyrins and heme proteins, all of these mechanisms can contribute to the excitation profiles, so they are quite complicated. Nevertheless, excitation profiles are powerful tools for studies of excited electronic states of heme and should be considered complementary to absorption spectroscopy for that purpose. By using this technique, one can readily see the difference between Fe(II)cytochrome c and Fe(II)-cytochrome bs. The difference is probably due to different mechanisms of energy transition for the two compounds (Friedman et al., 1977). Using Raman-excitation difference spectra, one can determine if there is a difference in the environments of the chromophores in the two heme proteins (Shelnutt, 1980a). 1.2.

ORIGINS OF VIBRATIONS

The vibrational modes of heme and porphyrins are extremely complicated and have been the subject of many investigations (Ogoshi et al., 1972; Stein et al., 1975; Susi and Ard, 1977; Rimai and Salmeen, 1978). Detailed vibrational modes of four types of symmetry and their frequencies can be seen in Figure 12.2 for Ni-octaethylporphyrin. The frequencies of these vibrational modes can be influenced by the iron spin state, the coordination geometry, and the peripheral substituents; therefore, the actual frequencies of different heme compounds vary slightly. Resonance-Raman-active vibrations of heme compounds can be grouped into A 19' A 2g , BIg' and B 2g , square-planar D 4h heme-molecule symmetry. Strictly speaking, hemes are not D 4h symmetrical, but most analyses start with D4h for convenience. As can be seen from

320

Hemes and Porphyrins

A,g

"'6

806

'i6

'is

A2g

lu;

z

w

z>-

FREQL£NCY

\

",

M

,

/E

c-c

I

\

c-c

C-c

E,C_\ 'H" I I /c-...,I I I I

",

/H

I

/C_r"'M

1'1- CU_N

"

SHIFT (em-')

I

I

'c-l

E/

I I

c_ /

I

E/

I"

/c_c/

N-CU-r-;

c-c........ 'c-c H/

\c

l- 'N . . -1

M,C/\

\:..-c,

HI'

'

I c-c

/ c

'c-I

N

E

I

C

,

M

c-c ...... 'c-c

\-1

H/

'H

'M

,

I

'

'H M

II

/ C-, c-!., /c-c

'\

H,

"'c_ I C

I

E/C-C

" j! c._ I I 'C-C'E HI

,

H-

l

-c/

J_c.. . . N'c_J

,,/

~_/

,I

III

'\

".H

'"

'H

/

c-c I \ /H c-c c-c

H,

,

I

'H/

I

'c-\ I le- cI'" I .M . . c_ I I 'c_ el H - C.-H

C

!_C",N,C_C 11/

I c-c I \, M \

IV

'H

,

,

M

FIGURE 12.4. Identification of Cu-etioporphyrins by resonance Raman spectroscopy. M, methyl; E, ethyl, and H, hydrogen atom. The figure was reproduced from Sunder et aI. (1975).

326

Hemes and Porphyrins

porphyrin plane (Babcock and Salmeen, 1979; Babcock et al., 1979a, b; Ondrias and Babcock, 1980; Babcock et al., 1981). The vibrational frequencies of the formyl group can be influenced by factors such as the spin state of the heme iron and the type of solvents used (Van Steelandt-Frentrup et al., 1981). The formyl C=O band appears at 1660 cm- I for reconstituted myoglobin whose heme is replaced by spirographis, isospirographis, or 2,4-diformylheme (Tsubaki et al., 1980). This frequency is slightly lower than that of cytochrome a 3 • Normal myoglobin, which contains protoheme IX without the formyl group, does not give the 1660-cm- I keto band. Cyanide ion often serves as an axial ligand, and it may also react with side-chain formyl groups. Likewise, NaHS0 3 may react with the formyl group; this too can be detected by Raman spectroscopy (Kitagawa et al., 1977b). However, this should be considered as a tentative interpretation of the experiments. There is other evidence showing that CN does not react with side-chain formyl (personal communication with Salmeen, 1981). 2.3.

IDENTIFICATION OF ISOMERS

Different side chains and their substitution at different positions may produce unique fingerprint regions in Raman spectra. Using these characteristic fingerprint regions, Raman spectroscopy can be used as an an:dytical tool. Many porphyrin isomers differ little and are not easily distinguished by conventional physicochemical methods. For instance, etioporphyrin has methyl and ethyl side chains. Isomers of etioporphyrins I, II, III, and IV differ only in the relative positions of these substituents. The resonance Raman spectra of the Cu complexes of these four isomers differ markedly in the 650-850 cm- 1 region (Figure 12.4) (Verma and Bernstein, 1974a; Sunder et al., 1975). Isomers of many other porphyrins have also been distinguished from each other by Raman spectroscopy (Verma and Bernstein, I974a).

3.

SPIN STATE

The Raman spectra of some heme proteins show characteristic spin-state marker bands, from which it is sometimes possible to determine the spin state of the iron. However, the effect of the spin state on resonance Raman spectra is an indirect one, which occurs via the perturbation of the porphyrin-ring 'IT-electron system. Thus sometimes Raman spin marker bands may not apply to all heme compounds. In this chapter the effects of spin state, ligands, and oxidation state will be discussed in separate sections. However, one should keep in mind that they are all interrelated. For instance, the spin state of iron can be altered by changes in ligand species.

,,.

Spin State

327

Before discussing the relationship between the spin state of heme iron and resonance Raman spectra, some basic information about spin state is briefly reviewed. 3.1.

SPIN

The electron has an inherent angular momentum called spin. Depending on the direction of spin of the electron, the Z-spatial component of the spin quantum number is assigned either + 1 or - 1. There are four quantum numbers to describe the state of an electron in an atom. Three designate a particular orbital, and the fourth designates one of two values of a spatial component of the spin angular momentum. Each electron must have a unique set of quantum numbers; therefore, only two electrons are allowed to occupy each set of orbitals, one with + 1 and one with spin - !. When all orbitals are occupied by paired electrons, the total spin state is zero. This is because the spin angular momenta of the two electrons with opposing spin quantum numbers of + ! and - ! cancel each other. If there is only one electron in an orbital, then the spin number is 1, and the atom shows paramagnetism. 3.2.

ELECTRONS IN THE COORDINATED IRON

Iron has an atomic number of 26 and contains 26 electrons, which are distributed in different electronic orbitals. They are the Is 2, 2s 2, 2 p6, 3s 2, 3p6, 3d 6 , and 4s 2 orbitals. When the iron atom loses two or three electrons it becomes Fe(II) or Fe(III) ion, respectively. 3d

Fe(II) Fe(III)

@CDCDCDCD CD CD CD CD CD

4s

o

o

4p

000 000

When iron forms a coordination complex, the electrons in the metal are relocated. The s orbital is spherical, and the p and d orbitals are shown in Figure 12.5. When a complex is formed, metal and ligand orbitals interact to form moleculer orbitals. For simplicity, only the interaction of the ligand (J orbitals with metal orbitals is discussed (Figure 12.6). Examples of such complexes include FeFl- and Co(NH3)~+ . The iron atom provides five 3d, one 4s, and three 4p orbitals. The f 2g (d XY ' d yz ' d zx ) orbitals will not interact with ligand a orbitals, so they are occupied by the electrons from the metal. The six ligands provide six orbitals that contain two electrons in each orbital. The interaction leads to the formation of bonding (e g , flU' a lg ) and antibonding (flU.' a]u.' ego) molecular orbitals. The electrons from ligands will not occupy antibonding molecular orbitals, but they will fill bonding orbitals. The

328

Hemes and Porphyrins z

5 -

orbital y

z

...

p- orbitals

~

z-

*

y

y

'~L

' ,,,,>-"•.- .,. : ';.

x

'''.:.

y

x

..... :-

Py

Pz

z

z

d-orbitals y dxz

y

y

x dx 2_ y2

FIGURE 12.5.

dz 2

Shapes of s, p, and d electron orbitals.

egO and l2g molecular orbitals have more metal character than other orbitals, and the l2g orbitals are occupied by electrons belonging to the iron atom. The six bonding molecular orbitals (e g , a'g' llu) actually retain considerable ligand character. The electrons (12 altogether) from ligands occupy the newly formed molecular orbitals e g , flu' and a'g' The electrons (6 for ferrous ion, 5 for ferric ion) from the metal fill the l2g and egO orbitals. If the energy difference between these two orbitals is large (the strong-field case), then all the electrons will fill the f 2g orbital first; only then will the egO orbital be filled. This will produce a low-spin complex, that is, 8 = t for Fe(III) or 8 = 0 for Fe(II). When the energy difference is small (the weak-field case), then the electrons enter the l2g and egO orbitals with their spins parallel (same sign). Thus a high-spin complex is formed (8 = 1 or 8 = 2 for Fe(III) and Fe(II), respectively).

....

I;

'l oj

~

ij 'l

. oj

I;

~

~

'"

§

"



0-

:;'

'e..

:::t

-* 0 :>

-


5145

III

'"

~~:ll:;:mg

.~

1-----

~

It'>

a

-

$

0

"

!!?

~I

'----.:.-.JL...

4579

It'>

tot1>

III

'"to-

It'>

a

It'>

t1>

III

~.

to-

;_N

I}

FIGURE 12.13. Examples of inverse polarization in cytochrome c. See the bands at l3l3 and 1585 cm- I when the compound is excited at 5145 A (top). The inverse polarization depends on the wavelength of laser excitation. See the 1313 and 1585 cm -1 bands at 4579-A excitation, the depolarization ratios become low (bottom). The figure was reproduced from Nafie et al. (1973).

6.3.

METALLOPORPHYRINS

The anomalously polarized Raman bands observed in heme compounds are also commonly found in other metalloporphyrins. The extent of anomalous polarization is unique for each compound, and it can be used to probe the structure of the chromophore in solution (Sunder et al., 1975; Asher and Sauer, 1976). Resonance Raman spectra of Ni(II)-, Co(II)-, and Cu(II)-mesoporphyrin IX dimethyl ester reveal that intensity (excitation-profile effect) and depolarization of Raman bands vary with the exciting wavelength. Anomalously polarized bands appear at 1305 and 1602 em-I for the Ni(II) compound, 1308 and 1597 em-I for the Co(II) derivative, and 1313 and 1581 cm- I for the Cu(II) compound (Verma et al., 1974). Ni, Cu, and Pd complexes of octamethylporphyrin and mesotetraphenylporphyrin also show several such anomalously polarized vibrations (Mendelsohn et aI., 1975). In spectra of copper porphin, such bands are found at 1322 and 1587 cm- I using an excitation line of 514.5 nm. Copper porphin has a unique structure with no peripheral substituents except hydrogen (Figure 12.14). It is interesting

Quarternary Structure 2

a

349

3

13

5 7

v

6

2

a

3

5 7

6

FIGURE 12.14. Structure of Cu·porphins (bottom) and porphin (top).

to observe that depolarization ratios for the two anomalously polarized bands remain constant at 45 and over all the exciting wavelengths in the a- and ,B-absorption regions, whereas some polarized bands show variation in their depolarization ratios (Verma and Bernstein, 1974c). 7.

QUATERNARY STRUCTURE

Biologically active hemoglobin is a tetramer. The mechanism of the cooperative oxygen binding of hemoglobin has been the subject of intensive study. The oxygen-binding curve of hemoglobin is sigmoidal; oxygenation becomes easier as the hemoglobin units in the tetramer become saturated. An important question arises concerning the mechanism of such an allosteric effect. Is the protein moiety responsible, or is there any change in heme structure? The primary structure of the four deoxyhemoglobin subunits is identical to that of the subunits of oxyhemoglobin, but they differ in quaternary structures, or in how the detailed protein three-dimensional structures are oriented in relation to each subunit. Two types of quaternary structure of methemoglobin have been proposed (Perutz, 1970). The T structure has low affinity for oxygen, whereas the R

350

Hemes and Porphyrins

structure has high affinity. There is a difference in the free energy of oxygen binding for the two structures. The difference in free energy is called the free energy of cooperativity and is about 3.6 kcal/mol. The T state is favored by deoxyhemoglobin and the R state is preferred by oxyhemoglobin. The cyrstal structures of ligated hemoglobins in the R form and deoxyhemoglobin in the T form do show the difference (Shelnutt, 1980b). In the R structure, the phenylalanine COl is in van der Waals contact (3.5 A) with the heme and very nearly parallel to it. The relative positions of phenylalanine residues of COl and G5 with respect to the heme for Rand T types of hemoglobins are shown in Figure 12.15. One question is where and how the free energy of cooperation is stored in the hemoglobin molecule. One speculation is that a particular bond is twisted or stretched, and this energy is released when the twisted bond is relaxed and extended. Frequently a metal-ligand bond is proposed to carry such an enhanced tension (Hoard and Scheidt, 1973). However, there is no experimental proof to indicate the presence of such a bond (Hopfield, 1973; Scholler et ai., 1976; Kincaid et ai., 1979a, b; Scholler and Hoffman, 1979a, b; Warshel and Weiss, 1981).

G5

~" G5

~ DEOXY

LIG NDED

COl

ALPHA CHAINS

"'"'~'"'"

~~EOY COl

LIGA OED

BETA CHAINS

FIGURE 12.15. Positions of phenylalanine side chains (G5 and CDI) with respect to the heme in the R (carbonmonoxyhemoglobin) and T structures (deoxyhemoglobin). The figure was reproduced from the abstract for Shelnutt (1980), who obtained it from Cyrus Chothia. Permission to reproduce the figure was granted by Dr. Chothia.

~

auarternary Structure

351

The addition of inositol hexaphosphate to nitrosylhemoglobin (HbNO) changes its visible and uv spectra significantly, whereas no effect is observed with HbOz. IHP is believed to stabilize the T structure. This is thought to be due to a strong interaction between the IHP and deoxy-HbNO that is not present with oxy-HbNO. This may stabilize deoxy-HbNO in the presence of IHP. It was found that there is a significant intensity change in the Raman band at 1643 cm -I and a decrease in the intensity of the 1633-cm- I band. Apparently these two bands are sensitive to changes in the quarternary structure of the protein (Szabo and Barron, 1975). The addition of IHP induces a change from the R to T quaternary structure of HbNO. Under this condition, the ,B-chains maintain the hexacoordinate structure of ImFeNO, whereas the a-chains are pentacoordinates with the FeNO (Maxwell and Caughey, 1976). The resonance Raman spectrum indicates that a new band at 592 cm- I (Fe-NO stretching) is produced in addition to the 553-cm- 1 Fe-NO band observed without IHP. This suggests that iron-imidazole bonds are broken in the a-chains in the T quaternary structure (Stong et aI., 1980). Quaternary structures of aquomethemoglobin and fluoromethemoglobin are also changed by the addition of IHP. The IHP changes the allosteric equilibrium of high-spin methemoglobin derivatives in favor of the T state (Perutz et aI., 1974). It is reported that the change in quaternary structure alters the equilibrium of high-spin and low-spin azidomethemoglobin from 10/90 to 45/55% (Scholler and Hoffman, 1979a, b). There have been several attempts to resolve quaternary-structure differences by resonance Raman spectroscopy. In order to see whether Raman spectroscopy can detect changes in quaternary structure induced by IHP, the protein structurally sensitive line at 1370 cm- 1 was examined (Rousseau et aI., 1980a). In all liganded methemoglobins known to have a change in quaternary structure, the frequency of the 1370-cm - I line decreases. In those in which no quaternary-structure change occurs, such as met HbA(Im-) and met HbA(Nj), the frequency difference is very small (Rousseau et aI., 1980b). When the sample was excited at 441.6 nm, which is close to the Soret band, only the T form of methemoglobin was partially photoreduced (Kitagawa and Nagai, 1979). Thus the two different quaternary-structure forms have different chemical reactivities. It is reported that the Fe(II)-N(histidine) band at 206 cm- 1 and a peripheral-group bending mode at 348 cm -I are also sensitive to the quaternary-structure change (Hori and Kitagawa, 1980; Nagai et aI., 1980a, b, c; Nagai and Kitagawa, 1980). When HbCO is photolyzed, the original 214-cm- 1 band shifts to 225 cm- I. Since the 214-cm- 1 band is close to the 206-cm- 1 band, it is speculated that a conformational change of hemoglobin may have occurred, for the early period of photodissociation, from 30 ps to 20 ns (Irwin and Atkinson, 1981). The resonance Raman spectral difference observed for deoxy Rand T structures is possibly due to the protein environment, but interaction between

352

Hemes and Porphyrins

the protein structure and the heme via the axial ligand is not ruled out (Shelnutt et al., 1979a, b).

8.

PROTEIN ENVIRONMENT

Resonance Raman spectra of heme proteins arise from heme vibrational modes. There are conflicting reports on whether the protein environment affects the resonance Raman spectra. If proteins do not affect the porphyrin ring, then they should show the same Raman spectra as long as the heme components are identical. On the other hand, if the apoprotein moiety influences the electronic-charge density on the porphyrin ring, then it will affect the spectra. Some investigators concluded that resonance Raman spectra do not reflect changes in the protein environment (Loehr and Loehr, 1973; Woodruff et al., 1975; Spiro et al., 1978; Spiro and Burke, 1976). Differences in Raman frequencies of heme proteins that contain the same heme group are indeed small. These small differences are attributed by some investigators to differences in the proteins' environment (Kitagawa and lizuka, 1974; Adar and Erecinska, 1974; Yamamoto et al., 1976). When cytochrome c from different species (horse, cow, dog, pigeon, spider monkey, turtle, human, tuna, baker's yeast, Candida krusei, Rhodospiri/lum rubrum) is examined, there are small (0-6 cm -1) frequency differences in the heme vibrational modes (Shelnutt et al., 1979a; 1981). Similarly, chemically modified (on an argInine residue) human deoxyhemoglobin has come up to 2.2-cm- I difference at 1567 cm- I compared with the unmodified compound (Shelnutt et al., 1979b). These differences are attributed to the effect of the protein moiety. In NMR, heme resonances vary only when there is a large change in the protein environment (Keller and Wuthrich, 1978). A dramatic change takes place in the vibrational properties of the FeN(histidine) bond when deoxyhemog10bin is frozen. This probably suggests that the protein interacts with water and affects the quaternary structure which in turn influences the Fe-N bond (Ondrias et al., 19&1).

9.

GEOMETRY OF THE HEME RING

There are a number of Raman active-modes that are sensitive to the geometry of the heme. A particularly important one is the anomalously polarized line at about 1590 cm- I . The type of ligand has a great influence on the position of iron with respect to the porphyrin plane. In the absence of a sixth ligand (pentacoordinated complex), the iron atom is out of plane. With a sixth ligand (hexacoordinated complex), the iron atom is pulled in the opposite direction by the sixth ligand (Figure 12.16). So whether or not the iron is in the plane of the porphyrin depends on the relative effects of the fifth and sixth ligands on the iron atom.

~

Geometry of the Heme Ring

/ L-Fe

\

L

I

L-Fe-L

I

353

FIGURE 12.16. Position of the central iron atom in pentacoordinated (left) and hexacoordinated (right) complexes.

There are two hypotheses concerning the geometry of the heme ring. The doming model was proposed by Spiro and his co-workers (Spiro and Strekas, 1974; Stein et al., 1975). According to this model, the central iron atom is situated out of plane to the heme and located above the porphyrin plane. However, there is no clear evidence that the heme is considerably "domed" in deoxyhemoglobin or other high-spin heme proteins (Yu, 1977). According to core expansion theory (Spaulding et al., 1975), the iron atom may stay in the center of the porphyrin ring, but the ring expands and shrinks. As the ring shrinks, the iron atom moves above the plane of the porphyrin ring. The 1590-cm- 1 (1580-1610 cm- I ) line is structurally sensitive in metalloporphyrin spectra, and there is an empirical correlation between its frequency and the distance from the center of the porphyrin core to the pyrro1e nitrogen atoms, d(C/-N) (Felton et al., 1974; Spaulding et al., 1975) (Figure 12.17). This structurally sensitive line is anomalously polarized (Spiro and Strekas, 1972). The line may arise from stretching and bending of the methine-bridge bonds. According to the core expansion model, an increase in the C/-N distance corresponds to a linear decrease in this frequency (1580-1610 cm -I). Using this plot, Lanir et al. (1979) came to the conclusion that the distance C/-N is 2.033 ± 0.01 A at acidic pH. X-ray diffraction study of diaquo( a, {3, 'I, c5-tetraphenylporphinato)Fe(III)-perchlorate, an iron porphyrin

FIGURE 12.17. Position of central iron atom in heme, where d(C,-N) is defined as the distance between the center of the porphyrin core and the pyrrole nitrogen. The figure was reproduced from Spaulding et al. (1975) with permission of the copyright owner, American Chemical Society.

354

Hemes and Porphyrins

with two weak-field axial ligands, showed that the average Fe-N-bond distance in this heme model is only 2.04 A (Kastner et aI., 1978). The short distance of the Fe-N bond in cytochrome c high-spin hemes with two weak axial ligands can only be explained if the iron(III) lies in plane with the heme. Myoglobin forms a stable complex with hydrogen peroxide in the pH range 8-9. In order to study the nature of the complex, Campbell et aI. (1980) examined Raman spectra of complexed and uncomplexed myoglobin. The distances from the iron to the pyrrol~ nitrogen (Fe-Np ) and the imidazole nitrogen (Fe-N im ) are 2.08 and 2.09 A, respectively, according to stretchingvibration bands at 345 and 375 cm -I and from the available X-ray data. The distance from the center of the porphyrin to the pyrrole nitrogen atoms Cr-N, as estimated from the 1560-1590-cm- 1 bands, is 2.01 A. There is X-ray evidence to indicate that core expansion takes place in some compounds. For instance, in (meso-tetraphenylporphinato)bis(tetrahydrofurna)-Fe(II), the iron atom is centered in the porphyrin plane, causing a greater amount of radial core expansion than observed in other iron porphyrin structures (Reed et aI., 1980). This is a rather interesting exception, because high-spin Fe(lI) porphyrins are usually pentacoordinated complexes, with large out-of-plane iron displacement. Deoxyhemoglobin has high-spin Fe(II) and is a pentacoordinated complex in which the iron atom lies substantially out of plane to the porphyrin. It is known that the transition of the R to the T quaternary stfllcture in carp azidemethemoglobin accompanies the change of spin state from low to high. The change in the high-frequency region of 1300-1700 cm- I reflects the change of spin states. The low-frequency band changes from 270 to 263 cm -I. This band is sensitive to the iron-heme plane distance (Desbois et aI., 1980). Instead of the anomalous polarized line near 1590 cm- 1 that appears in the spectra of compounds, a line appears at the unusually low frequency of 1550 cm - I in spectra of leghemoglobin, which is found in the nitrogen-fixing bacteria in legume root nodules. This indicates an expanded porphyrin core in leghemoglobin (Armstrong et aI., 1980). The iron of hemoglobin can be replaced with cobalt(lI) without loss in the hemoglobin's ability to bind oxygen. Deoxy-Co(lI)Hb is low spin. In hexacoordinated Co(lI)-porphyrin, the cobalt atom is small enough to stay in the center of the porphyrin-ring plane (Woodruff et aI., 1974). An important question is what factor makes the core expand. The conclusion of Spiro et aI. (1979) is that the core size is probably due to the effect of axial ligands.

10.

MITOCHONDRIA

Oxidation is an important process in metabolism. Most of the foodstuffs such as the carbohydrates and lipids that we eat are highly reduced compounds. Metabolism of these compounds involves mainly the removal of hydrogens or

Mitochondria

355

electrons using molecular oxygen as the final electron acceptor (or hydrogen acceptor). This involves a series of electron carriers, and during this process ATP is produced through oxidative phosphorylation in mitochondria. Substrate

10.1.

->

NAD

->

cyt c

->

->

flavin coenzyme

->

cyt (a + a3) cytochrome oxidase

coQ

->

->

cytb

->

cytc]

O2

INTACT MITOCHONDRIA

Resonance Raman spectra of intact reduced mitochondria were obtained by Adar and Erecinska (1978) (Figure 12.18). They were able to identify the contributions from the individual cytochromes and to monitor the physical and biochemical states of hemes in biologically active membranes. The intensity of Raman spectra depends on the excitation wavelength relative to the peak positions of the a-, {3-, and y-absorption bands of cytochromes. Isolated cytochrome b has marker bands at 1306, 1342, 1538, and 1564 cm- I . In this membrane system, these bands shifted to lower frequencies. Incidentally, the formation of the cytochrome b-c, complex shifts these marker bands to lower frequencies. 10.2.

CYTOCHROMES bAND c

When the cytochrome b-c] complex is excited at 531 nm, there are anomalous features in the Raman spectra that are explained as interactions between band c-type hemes in the membrane preparation. For instance, one of the marker bands (1297 cm - I) is low compared with the usual position at 1305-1340 cm- I in other proteins containing heme b. The other marker band .... to

~u' 441Gnm

~

5

"£

!2

...., ....

T transition on the resonance Raman spectra of carp azide methemoglobin. In Proc. VIJth Tnt. Conf. Raman Spectrosc., W. F. Murphy, Ed., North-Holland, Amsterdam and New York, pp. 576-577. Desbois, A., Momenteau, M., Loock, B., and Lutz, M. (1981). Assignment of N(pyrrole)-sensitive Raman bands of 2-methylimidazole and bisimidazole complexes of ferroetioporphyrin. Spectrosc. Lell. 14, 257. Duff, L. L., Appelman, E. H., Shriver, D. F., and Klotz, I. M. (1979). Steric disposition of O 2 oxyhemoglobin as revealed by its resonance Raman spectrum. Biochem. Biophys. Res. Commun.90, 1098. Felton, R. H., Yu, N.-T., O'Shea, D. C., and Shelnutt, 1. A. (1974). Structural implication in metalloporphyrins of the 1590-cm- 1 anomalously polarized resonance Raman line. J. Am. Chem. Soc. 96, 3675. Felton, R. H., Romans, A. Y., Yu, N.-T., and Schonbaum, G. R. (1976). Laser Raman spectra of oxidized hydroperoxidases. Biochim. Biophys. Acta 434, 82. Ferrone, F. A., and Topp, W. C. (1975). Circular dichroism and Raman studies of the allosteric transition in methemoglobin. Biochem. Biophys. Res. Commun. 66, 444.

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362

Hemes and Porphyrins

Kincaid, J., Stein, P., and Spiro, T G. (I 979a). Absence of heme-localized strain in T state hemoglobin: insensitivity of heme-imidazole resonance Raman frequencies to quaternary structure. Proc. Nat. Acad. Sci. 76, 549. Kincaid, 1., Stein, P., and Spiro, T G. (1979b). Absence of heme-localized strain in T state hemoglobin: insensitivity of heme-imidazole resonance Raman frequencies to quaternary structure (correction). Proc. Nat. Acad. Sci. 76, 4156. Kitagawa, T, and Iizuka, T (1974). Resonance Raman spectra of heme proteins. Seihlltsll.Butsuri 14,272. Kitagawa, T, and Nagai, K. (1979). Quaternary structure-induced photoreduction of haem of haemoglobin. Nature 281, 503. Kitagawa, T and Orii, Y. (1978). Resonance Raman studies of cytochrome oxidase. J. Biochem. 84, 1245. Kitagawa, T., and Orii, Y. (1979). Two kinds of the oxidized state of cytochrome oxidase studied by resonance Raman spectra. In Developments in Biochemistry,S: Cytochrome Oxidase, T E. King, Y. Orii, B. Chance, and K. Okunuki, Eds., Elsevier/North-Holland Biomedical Press, Amsterdam, pp. 129-138. Kitagawa, T, Kyogoku, Y., Iizuka, T., Ikeda-Saito, M., and Yamanaka, T (1975a). Resonance Raman scattering from hemoproteins. Effects of ligands upon the Raman spectra of various C-type cytochromes. J. Biochem. 78, 719. Kitagawa, T., Ogoshi, H., Watanabe, E., and Yoshida, Z. (I 975b). Resonance Raman scattering from metalloporphyrins. Metal and ligand dependence of the vibrational frequencies of octaethylporphyrins. J. Phys. Chem. 79, 2629. Kitagawa, T., Ogoshi, H., Watanabe, E., and Yoshida, Z. (1975c). Resonance Raman spectra of metalloporphyrins. On the methine-bridge vibrations of ferric octaethylporphyrins and its a', f3', y', and fj' deutero derivatives. Chem. Phys. Lett. 30, 451. Kitagawa, T., Abe, M., Kyogoku, Y, Ogoshi, H., Watanabe, E., and Yoshida, Z. (I 976a). Resonance Raman spectra of metallooctaethylporphyrins. Low frequency vibrations of porphyrin and iron-axial ligand stretching modes. 1. Phys. Chem. SO, 1181. Kitagawa, T., Kyogoku, Y., Iizuka, T., and Saito, M. 1. (I 976b). Nature of the iron-ligand bond in ferrous low spin hemoproteins studied by resonance Raman scattering. 1. Am. Chem. Soc. 98, 5169. Kitagawa, T, Abe, M., Kyogoku, Y., Ogoshi, H., Sugimoto, H., and Yoshida, Z. (1977a). Resonance Raman spectra of ISN enriched metallooctaethyloporphyrins. Characterization of the oxidation state marker bands of hemoproteins. Chem. Phys. Lett 48, 55. Kitagawa, T., Kyogoku, Y., and Orii, Y. (l977b). Resonance Raman spectra of heme a derivatives. Evidence for the reaction of peripheral formyl group with HCN and NaHS0 3 . Arch. Biochem. Biophys. 181, 288. Kitagawa, T., Ozaki, Y, Kyogoku, Y, and Horio, T (I 977c). Resonance Raman study of the pH-dependent and detergent-induced structural alterations in the heme moiety of Rhodospirillum ruhrum cytochrome c'. Biochim. Biophys. Acta 495, I. Kitagawa, T., Ozaki, Y., Teraoka, 1., Kyogoku, Y., and Yamanaka, T (1977d). The pH dependence of the resonance Raman spectra and structural alterations at heme moieties of various c-type cytochromes. Biochim. Biophys. Acta 494, 100. . Kitagawa, T., Ozaki, Y, and Kyogoku, Y (1978). Resonance Raman studies on the ligand-iron interactions in hemoproteins and metallo-porphyrins. Adv. Biophys. ll, 153. Kitagawa, T, Nagai, K., and Tsubaki, M. (1979). Assignment of the Fe-N. (His F8) stretching band in the resonance Raman spectra of deoxy myoglobin. FEBS Lett. 104, 376. Lanir, A., and Aviram, 1. (1975). Proton magnetic relaxation and anion effect in solutions of acid ferricytochrome c. Arch. Biochem. Biophys. 166,439. Lanir, A., Yu, N.-T., and Felton, R. H. (1979). Conformational transitions and vibronic couplings in acid ferricytochrome c: A resonance Raman study. Biochemistry 18, 1656.

j.

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Loehr, T. M., and Loehr, 1. S. (1973). Determination of oxidation and spin states of heme iron. Resonance Raman spectroscopy of cytochrome c, microperoxidase, and horseradish peroxidase. Biochem. Biophys. Res. Cornman. 55, 218. Lyons, K. B., Friedman, 1. M., and Fleury, P. A (1978). Nanosecond transient Raman spectra of photolysed carboxyhaemoglobin. Nature 275, 565. Maxwell, 1. c., and Caughey, W. S. (1976). An infrared study of NO binding to heme Band hemoglobin A Evidence for inositol bexaphosphate induced cleavage of proximal histidine to iron bonds. Biochemistry 15, 388. Maxwell, J. c., Volpe, 1. A, Barlow, C. H., and Caughey, W. S. (1974). Infrared evidence for the mode of binding of oxygen to iron of myoglobin from heart muscle. Biochem. Biophys. Res. Commun.58, 166. Mendelsohn, R., Sunder, S., and Bernstein, H. J. (1975). Resonance Raman studies of 2,3,3,4,5,6,7,8-octamethylporphin, 1,3,5, 7-tetramethylporphin, and mesotetraphenylporphin and its Ni-, Cu-, and Pd-chelates. J. Raman Spectrosc. 3, 303. Myer, Y. P., and Bullock, F. A (1978). Cytochrome bS62 from Escherichia coli: Conformational, configurational, and spin-state characterization. Biochemistry 17, 3723. Nafie, L. A, Pezolet, M., and Peticolas, W. L. (1973). On the origin of the intensity of tbe resonance Raman bands of differing polarization in heme proteins. Chern. Phys. Leu. 20, 563. Nagi, K., and Kitagawa, T. (I 980f. Differences in Fe(II)-N.(His-F8) stretching frequencies between deoxyhemoglobins in the two alternative quaternary structures. Proc. Nat. Acad. Sci. 77, 2033. Nagai, K., Enoki, Y., and Kitagawa, T. (I 980a). Influence of quaternary structure on the state of berne in carp and human methemoglobins studied by resonance Raman scattering. Biochim. Biophys. Acta 624, 304. Nagai, K., Kitagawa, T., and Morimoto, H. (I 980b). Quaternary structures and low frequency molecular vibrations of baems of deoxy and oxy-haemoglobin studied by resonance Ranjan scattering. J. Mol. Bioi. 136,271. Nagai, K., Welborn, c., Dolphin, D., and Kitagawa, T. (1980c). Resonance Raman evidence for cleavage of the Fe-N.(His-F8) bond in the IX subunit of the T-structure nitrosylhemoglobin. Biochemistry 19, 4755. Nagumo, M., Nicol, M., and EI-Sayed, M. (1981). Polarized resonance Raman spectroscopy of the photointermediate of oxyhemoglobin on the picosecond time scale. J. Phys. Chern. 85, 2435. Ogoshi, H., Saito, Y., and Nakamoto, K. (1972). Infrared spectra and normal coordinate analysis of metalloporphins. J. Chern. Phys. 57,4194. Ogoshi, H., Sugimoto, N, and Yoshida, Z.-!. (1980). IH-NMR and resonance Raman spectra of octaethylporpbyrinatoiron(III) perchlorate and its monoimidazole adduct. Biochim. Biophys. Acta 621, 19. Ondrias, M. R., and Babcock, G. T. (1980). Resonance enhancement of the vibrations of cytochrome a3 and its conformation in oxidized cytochrome oxidase. Biochem. Biophys. Res. Commun. 93, 29. Ondrias, M. R., Rousseau, D. L., and Simon, S. R. (1981). Structural changes at the heme induced by freezing hemoglobin. Science 213, 657. Osterlund, K., and Sievers, G. (1981). Axial ligands of the heme iron in soybean legbemoglobin a as investigated using resonance Raman spectroscopy. Acta Chern. Scand. Ser. B. 35, 83. Osterlund, K., Sievers, G., and Nuotio, L. (1979). Resonance Raman spectroscopy of some hemoproteins. In Proc. Nat. Mtgs. Biophys. Eng. Finland, A3, pp. 1-4. Ozaki, Y., Kitagawa, T., and Kyogoku, Y. (I 976a). Raman study of the acid-base transition of ferric myoglobin; direct evidence for the existence of two molecular species at alkaline pH. FEBS Leu. 62, 369. Ozaki, Y., Kitagawa, T., Kyogoku, Y., Shimada, H., Iizuka, T., and Ishimura, y. (I 976b). An anomaly in the resonance Raman spectra of cytochrome P-450cam in the ferrous high-spin state. J. Biochem. SO, 1447.

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Ozaki, Y., Kitagawa, T., Kyogoku, Y., Imai, Y., Hashimoto-Yutsudo, C., and Sato, R. (1978). Resonance Raman studies of hepatic microsomal cytochromes P-450: Evidence for strong '1T basicity of the fifth ligand in the reduced and carbonyl complex forms. Biochemistry 17, 5826. Padlan, E. A, and Eaton, W. A (1975). A crystallographic study of deoxycolbalt (II) mesoporphyrin. IX. Myoglobin. J. Bioi. Chem. 17, 7069. Perutz, M. F. (1970). Stereochemistry of cooperative effects in haemoglobin. Nature 228,726. Perutz, M. F., Fersht, A R., Simon, S. R., and Roberts, G. C. K. (1974). Influence of globin structure on the state of the heme. II. Allosteric transitions in methemoglobin. Biochemistry 13,2174. Pettigrew, G. W., Leaver, J. L., Meyer, T. E., and Ryle, A P. (1975). Purification, properties and amino acid sequence of atypical cytochrome c from two protozoa, Euglena gracilis and Crithidai oncopelti. Biochem. J. 147, 291. Pezolet, M., Nafie, L. A, and Peticolas, W. L. (1973). Complete polarization measurements for non-symmetric Raman tensors: Symmetry assignments of ferrocytochrome c vibrations. J. Raman Spectrose. 1, 455. Rakshit, G., and Spiro, T. G. (1974). Resonance Raman spectra of horseradish peroxidase: Evidence for anomalous heme structure. Biochemistry 13, 5317. Rakshit, G., Spiro, T. G., and Uyeda, M. (1976). Resonance Raman evidence for Fe(IY) in compound II of horseradish peroxidase. Biochem. Biophys. Res. Commun. 71, 803. Reed, C. A, Mashiko, T., Scheidt, W. R., Spartalian, K., and Lang, G. (1980). High-spin iron(II) in the porphyrin plane. Structural characterization of (meso-tetraphenylporphinato)bis(tetrahydrofuran) iron(II). J. Am. Chem. Soc. 102,2302. Remba, R. D., Champion, P. M., Fitchen, D. B., Chiang, R., and Hager, L. P. (1979). Resonance Raman investigations of chloroperoxidase, horseradish peroxidase and cytochrome c using ' Soret band laser excitation. Biochemistry 18, 2280. Rimai, L, and Salmeen, I. (1978). Normal coordinate models for heme Raman spectra; uses and limitations. In Frontiers of Biological Energetics, Vol. I, Academic, New York, pp. 600-607. Ronnberg, M., Osterlund, K., and Ellfolk, N. (1980). Resonance Raman spectra of Pseudomonas cytochrome c peroxidase. Biochim. Biophys. Acta 626, 23. Rousseau, D. L., Shelnutt, 1. A, and Simon, S. R. (1980a). Methemoglobin imidazole: Evidence against an IHP-induced change in quaternary structure. FEBS Lett. 111, 235. Rousseau, D. L., Shelnutt, J. A, Henry, E. R., and Simon, S. R. (I 980b). Raman difference spectrsocopy of tertiary and quaternary structure changes in methaemoglobins. Nature 285, 49. Salmeen, I., Rimai, L., Yamamoto, T., Palmer, G., Hartzell, C..R., and Beinert, H. (1973). Resonance Raman spectroscopy of cytochrome c oxidase and electron transport particles with excitation near the Soret band. Biochem. Biophys. Res. Commun. 52, 1100. Salmeen, I., Rimai, L., and Babcock, G. (I 978a). Raman spectra of heme a, cytochrome oxidase-ligand complexes, and alkaline denatured oxidase. Biochemistry 17, 800. Salmeen, I., Rimai, L., and Babcock, G. T. (l978b). Heme a models for cytochromes a and a3 in cytochrome oxidase resonance Raman studies. In Frontiers of Biological Energetics, Vol. 2, P. L. Dutton, J. S. Leigh, and A Scarpa, Eds., Academic, New York, pp. 905-911. Scholler, D. M., and Hoffman, B. M. (I 979a). Resonance Raman and EPR of carp hemoglobin: Sensitivity of spectroscopic probes to heme strain. In Porphyrin Chemistry Advances, Papers from the Porphyrin Symposium, 1977, F. R. Longo, Ed., Ann Arbor Science., Ann Arbor, Mich., pp. 315-333. Scholler, D. M., and Hoffman, B. M. (I 979b). Resonance Raman and electron paramagnetic resonance studies of the quaternary structure change in carp hemoglobin. Sensitivity of these spectroscopic probes to heme strain, J. Am. Chem. Soc. 101, 1655. Scholler, D. M., Hoffman, B. M., and Schriver, D. F. (1976). Resonance Raman spectra of liganded and unliganded carp hemoglobin in both R and T states. J. Am. Chem. Soc. 98, 7RI'il'i

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Spiro, T. G., Stong, 1. D., and Stein, P. (1979). Porphyrin core expansion and doming in heme proteins. New evidence from Raman spectra of six-coordinate high-spin iron(III) hemes. J. Am. Chem. Soc. 101,2648. Srivastava, R. 8., Pace, C., and Yu, N.-T. (1981). Comparative Raman studies of cytochrome bS62 and cytochrome c. J. Raman Specfrose. 11, 20. Stein, P., Burke, 1. M., and Spiro, T. G. (1975). Structural interpretation of heme protein resonance Raman frequencies. Preliminary normal coordinate analysis results. J. Am. Chem. Soc. 97, 2304. Stein, P., Mitchell, M., and Spiro, T. G. (1980). Hydrogen-bond and deprotonation effects on the resonance Raman iron-imidazole mode in deoxyhemoglobin models: Implications for hemoglobin cooperativity. J. Am Chem. Soe. 102, 7795. Stein, P., Terner, 1., and Spiro, T. G. (1982). Hemoglobin R-state iron-imidazole frequency observed by time-resolved resonance Raman spectroscopy. J. Phys. Chem. 86, 168. Stong, J. D., Burke, 1. M., Daly, P., Wright, P., and Spiro, T. G. (1980). Resonance Raman spectra of nitrosyl heme proteins and of porphyrin analogues. J. Am. Chem. Soc. 102,5815. Strekas, T. c., and Spiro, T. G. (I 972a). Cytochrome c: Resonance Raman spectra. Biochim. Biophys. Acfa 278, 188. Strekas, T. C., and Spiro, T. G. (I 972b). Hemoglobin: Resonance Raman spectra. Biochim. Biophys. Acta 263,830. Strekas, T. c., and Spiro, T. G. (1974). Resonance-Raman evidence for anomalous heme structures in cytochrome c' from Rhodopseudomonas palustris. Biochim. Biophys. Acta 351, 237. Stryer, L., Kendrew, 1. c., and Watson, H. C. (1964). The mode of attachment of the azide ion to sperm whale metmyoglobin. J. Mol. BioI. 8, 96. Sunder, S., Mendelsohn, R., and Bernstein, H. 1. (1975). Resonance Raman. spectra of CuI: 3: 5: 7-tetramethylporphin and Cu-I: 2: 3: 4: 5: 6: 7: 8-octamethyl p~rphin. J. Am. Chem. Phys. 63, 573. Susi, H., and Ard, J. S. (1977). A valence force field for nickel porphin and copper porphin. Spectrochimica Acfa 33A, 561. Szabo, A, and Barron, L. D. (1975). Resonance Raman studies of nitric oxide. J. Am. Chem. Soc. 97,660. Teraoka, 1., and Kitagawa, T. (1980a). Resonance Raman study of the heme-linked ionization in reduced horseradish peroxidase. Biochem. Biophys. Res. Commun. 93, 694. Teraoka, 1., and Kitagawa, T. (I 980b). Raman characterization of axial ligands for penta- and hexacoordinate ferric high- and intermediate-spin (octa-ethylporphyrinato) iron(I1I) complexes. Eluicidation of unusual resonance Raman spectra of cytochrome c'. J. Phys. Chem. 84, 1928. • Teraoka, 1., and Kitagawa, T. (1981). Structural implication of the heme-linked ionization of horseradish peroxidase probed by iron-histidine stretching Raman line. J. BioI. Chem. 256, 3969. Temer, 1., Spiro, T. G., Nagumo, M., Nicol. M. F., and EI-Sayed, M. A (1980). Resonance Raman spectroscopy in the picosecond time scale: The carboxyhemoglobin photointermediate. J. Am. Chem. Soc. 102, 2328. Terner, 1., Stong, 1., Spiro, T. G., Nagumo, M., Nicol, M., and EI-Sayed, M. A (1981). Picosecond resonance Raman spectroscopic evidence for excited-state Spin conversion in carbon monoxyhemoglobin photolysis. Proc. Nat. Acad. Sci. USA 78, 1313. Thoai, P.-V., Leickman, 1. P., Momenteau, M., and Loock, B. (1979). Resonance Raman scattering from (14/15)N-(24/26)Mg-etioporphyrins I. Specfrosc. Lett. 12,333. Tsubaki, M., and Yu, N. (1981). Resonance Raman investigation of dioxygen bonding in oxycobaltmyoglobin and oxycobalthemoglobin: Structural implication of splitting of the bound oxygen-oxygen stretching vibration. Proc. Nat. Acad. Sci. 78, 3581.

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Tsubaki, M., and Yu, N.-T. (1982). Resonance Raman investigation of nitric oxide bonding in nitrosylhemoglobin A and -myoglobin: Detection of bound N-O stretching and Fe-NO stretching vibrations from the hexacoordinated NO-heme complex. Biochemistry 21, 1140. Tsubaki, M., Nagai, K, and Kitagawa, T. (1980). Resonance Raman spectra of myoglobins reconstituted with spirographis and isospirographis hemes and iron 2,4-diformylprotoporphyrin. IX. Effect of formyl substitution at the heme periphery. Biochemistry 19, 379. Tsubaki, M., Srivastava, R. B., and Yu, N.-T. (1981). Temperature dependence of resonance Raman spectra of metmyoglobin and methemoglobin azide vibrations and iron-azide stretch. Biochemistry 20, 946. Tsubaki, M., Srivastava, R. B., and Yu, N.-T. (1982). Resonance Raman investigation of carbon monoxide bonding in (carbon monoxy) hemoglobin and -myoglobin: Detection of Fe-CO stretching and Fe-C-O bending vibrations and influence of the quaternary structure change. Biochemistry 21, 1132. Van Steelandt-Frentrup, J., Salmeen, I., and Babcock, G. (1981). A ferrous, high-spin heme a model for cytochrome a3 in the dioxygen reducing site of cytochrome oxidase. J. Am. Chem. Soc. 103, 5981. Verma, A L. (1976). Effect of peripheral substituents on resonance Raman spectra of metalloporphyrins and heme proteins. In Proc. Tnt. Conf. Raman Spectrose., 5th, E. D. Schmid, J. Brandmueller, and W. Kiefer, Eds., Hans Ferdinand Schulz Verlag, FreiburgjBr., Germany, pp. 198-199. Verma, A L., and Bernstein H. 1. (1974a). Resonance Raman spectra of metal-free porphin and some porphyrins. Biochern. Biophys. Res. Commun. 57, 255. Verma, A L., and Bernstein, H. 1. (1974b). Resonance Raman spectra of protohemin and protohemin-imidazole complex. J. Raman Spectrose. 2, 163. Verma, A L., and Bernstein, H. J. (1974c). Resonance Raman spectra of copper-porphin. .I. Chem. Phys. 61, 2560. Verma, A L., Mendelsohn, R., and Bernstein, H. 1. (1974). Resonance Raman spectra of the nickel, cobalt and copper chelates of mesoporphyrin. IX. Dimethyl ester. J. Chern. Phys. 61, 383. Walters, M. A, Spiro, T. G., Suslick, K S., and Collman, J. P. (1980). Resonance Raman spectra of (dioxygen)(porphyrinato)(hindered imidazole) iron (II) complexes: Implications for hemoglobin cooperativity. J. Am. Chern. Soc. 102,6857. Warshel, A, and Weiss, R. M. (1981). Energetics of heme-protein interactions in hemoglobin. J. Am. Chem. Soc. 103,446. Woodruff, W. H., and Farquharson, S. (1978). Time-resolved resonance Raman spectroscopy of hemoglobin derivatives: Heme structure changes in 7 nanoseconds. Science 201, 831. Woodruff, W. H., Spiro, T. G., and Yonetani, T. (1974). Resonance Raman spectra of cobalt-substituted hemoglobin: Cooperativity and displacement of the cobalt atom upon oxygenation. Proc. Nat. Acad. Sci. 71, 1065. Woodruff, W. H., Adams, D. H., Spiro, T. G., and Yonetani, T. (1975). Resonance Raman spectra of cobalt myoglobins and cobalt porphyrins. Evaluation of protein effects on porphyrin structure, J. Am. Chem. Soc. 97, 1695. Woodruff. W. H., Dallinger, R. F., Antalis, T. M., and Palmer, G. (1981). Resonance Raman spectroscopy of cytochrome oxidase using Soret excitation: Selective enhancement, indicator bands, and structural significance for cytochromes a and a3' Biochemistry 20, 1332. Yamamoto, T., Palmer, G., Gill, D., Salmeen, I. T., and Rimai, L. (1973). The valence and spin state of iron in oxyhemoglobin as inferred from resonance Raman spectroscopy. J. Bio/. Chem. 248, 5211. Yamamoto, T., Palmer, G., and Crespi, H. (1974). Resonance Raman studies of a c type algal cytochrome. Biochim. Biophys. Acta 349, 232. -

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CHAPTER

Copper and other Metals in Biological Systems

1.

COPPER IN BIOLOGICAL SYSTEMS

There are many varieties of oxygen carriers in the animal kingdom. The most common and well known example is hemoglobin, which is found in all vertebrates and many invertebrates. Another iron-containing oxygen carrier is hemerythrin, which is a nonheme protein. The third major type is represented by copper-containing proteins the hemocyanins. Despite their common functions as molecular oxygen carriers, their chemical structures and properties are quite different. Copper is also found in many other proteins; cytochrome oxidase is a well-known example (Chapter 12, Sections 5 and 10). There are different copper sites in copper proteins and usually they are classified into three types, namely type 1, type 2, and type 3, based on their spectral properties. Type 1 copper sites are characterized by high absorbance near 600

370

Copper and Other Metals in Biological Systems

nm giving a deep blue color. Type 2 copper has less blue color. Type 3 Copper is less studied but the copper of this type in Rhus laccase is an antiferromagnetic-coupled cupric dimer. Ascorbate oxidase, polyphenoloxidase, tyrosinase, plastocyanin, amine oxidase, dopamine-,B-hydroxylase, and ceruloplasmin are all copper-containing enzymes. Copper-containing enzymes are the subject of intensive investigation using a variety of physical techniques such as ESR, CD, and absorption spectroscopy. Because of the relatively recent use of Raman spectroscopy in biological systems, fewer studies have been made using Raman spectroscopy. Despite this, Raman spectroscopy is becoming important in this field, and some important problems such as oxygen structure in oxyhemocyanin and the type of ligand in Cu-proteins have been studied by this technique. In this chapter, only the studies using Raman spectroscopy are reviewed.

1.1.

HEMOCYANIN

The blood of some nonvertebrates, such as the arthropods and mollusks, contains the blue pigment hemocyanin as the oxygen carrier. Hemocyanin is a metalloprotein containing 2 mol of copper per mole of protein. The molecular weight of hemocyanin is very large and ranges from half a million to over 10 million. One mole of copper binds to 2 mol of oxygen in a nonlinear fashion. There are several questions still to be answered concerning the oxidation state of the O2 in oxyhemocyanin and the oxidation state and arrangement of the two copper atoms. 1.1.1.

Oxygen in Hemocyanin

The oxygenated hemocyanin has a strong absorption band in the near uv at 350 nm and a weak band in the visible region at 570-580 nm. Thus one can obtain a resonance-enhanced spectrum of the blue-colored oxyhemocyanin by excitation with visible light such as 531-, 514.5-, 488-, 476.5-, and 457.9-nm laser lines. Both blue oxyhemocyanin and colorless deoxyhemocyanin are diamagnetic. The 570-580-nm absorption band is assigned to a charge-transfer transition of O{- to Cu(II) (Freedman et al., 1976). The origin of the 350-nm absorption band may be a simultaneous pair excitation (Larrabee et al., 1977). Oxygenation of hemocyanin produces two resonance-enhanced peaks at 742 and 282 em-I. The 742-cm- 1 peak is from the diatomic 0-0 stretching vibration determined by the replacement of 16 0 by 18 0, which causes a shift to 704 em-I. There is a small frequency difference in the peroxide (O{-) band depending on the source of hemocyanin. For instance, the vibration of this band is found at 744 em-I for arthropod hemocyanin, 749 em-I for mollusk hemocyanin (Freedman et al., 1976), 752 em-I for snail hemocyanin (Chen et al., 1979), and 741 em-I for the functionally active fragment (Gielens et al., 1980).

.J

':t

Copper in Biological Systems

CuliU -

0'0 _ CuUII

371

FIGURE 13.1. Simplified diagram of oxygen-binding site in oxyhemocyanin. The Cu-Oz-Cu is nonplanar and has JL-dioxygen-bridged geometry.

It is known that the stretching vibration of 0-0 is at 878 em -I for hydrogen peroxide (H 20 2 ) and at 738 em-I for Na 20 2 (Evans, 1969). If the O2

/

a

were the M- a type, the stretching vibration of 0-0 would occur around 1100-1140 em -I (Caughey et al., 1975; Szymanski et al., 1979). It is, therefore, reasonable to conclude that the bound oxygen is of the peroxide-ion type 01(Figure 13.1). A more-detailed model was proposed by Lontie and Gielens (1979) and is shown in Figure 13.2. The 282-cm- 1 peak is insensitive to isotopic substitution and is probably associated with the Cu-02 -Cu vibration (Loehr et al., 1974). The same conclusion was reached by Chen et al. (1979). However, the 282-cm- 1 band was assigned to the Cu(II)-imidazole stretching mode based on the frequency of the Cu(II)-imidazole complex as described by Larrabee et al. (1977). Further clarification of the assignment of this band is required. The 0-0 vibration of molecular oxygen appears at 1555 em-I, that of superoxide (a-a-H) at 1101 em-I, and that of peroxide (H-O-OH) at 878 em -I. Therefore, it is concluded that oxygen is bound as a peroxide ion in oxyhemocyanin. Tryptic fragments of hemocyanin retain the active site, as can be seen from the 0-0 stretching vibration (Gielens et al., 1980). Oxygen binding is an oxidative addition process in which O2 is reduced and the two Cu(II) centers of colorless deoxyhemocyanin are converted to the blue Cu(II) state (Thamann et al., 1977). 1.1.2.

Ligands

The Cu-N (imidazole) ligand vibration has been determined to be at 282 cm- I by a number of investigators (Table 13.2). For the functionally active fragment of tryptic hydrolysis, the Cu-N band was observed at 270 cm- l (Gie1ens et al., 1980). An excitation line in the visible region was used for most of the hemocyanin studies. The resonance spectrum of hemocyanin can be obtained by excitation at 350 cm -I. The 226- and 267-cm -I bands were assigned to Cu-N (imidazole) vibration modes; however, no Cu-O stretching mode was observed (Larrabee and Spiro, 1980). Addition of ethyleneglycol converts the blue color of oxyhemocyanin to purple. This suggests that some change occurs at or near the active site of

L 1m, / ' " ",1m Im-cu CU,lm Im/ '0-0..... 1m

FIGURE 13.2. A proposed model of the oxygen-binding site of oxyhemocyanin based on evidence from a combination of studies. 1m refers to the imidazole of histidine residues, and L refers to a bridging ligand, probably from a tyrosine residue. The figure was obtained from Lontie and Gielens, 1979.

372

Copper and Other Metals In Biological Systems

hemocyanin with the addition of ethyleneglycol. This color change takes place only with oxyhemocyanin and not with deoxyhemocyanin. Raman spectra of both purple and blue hemocyanins show a peroxide-dianion band around 750 cm -1, indicating that the color change is not due to the presence or absence of the peroxide dianion, but is probably due to a modification of the protein moiety, which eventually affects the copper active site (Mori et al., 1980; Nakahara et al., 1980). 1.2.

OTHER BLUE COPPER PROTEINS

There is a variety of copper-containing proteins with deep blue color due to their intense absorption near 600 nm. The intensities of the blue color are much stronger than those of simple cupric complexes. Tyrosinase is a copper-containing protein that interacts with molecular oxygen to hydroxylate monophenols. Oxytyrosinase and oxyhemocyanin have similar absorption and Raman spectra. The numerous low-frequency bands are probably due to the vibrational modes involving Cu-N and N-Cu-N. The 755-cm- t band originates from the 0-0 peroxide stretching vibration, as in the isotopic '80z-oxytyrosinase, the 755-cm- 1 band shifts to 714 cm- I • The copper atoms in oxytyrosinase are probably in a divalent state (Eickman et al., 1978). Stellacyanin isolated from the Japanese lac tree is a conj\Jgated protein containing mucopolysaccharides. It consists of 108 amino acid residues, 20% carbohydrate, and I mol of copper atoms. Ceruloplasmin is a plasma copper oxidase and has a blue color. A person with Wilson's disease has a low ceruloplasmin content. Ceruloplasmin and laccase contain six and four copper atoms, respectively. The intense absorption at 600 nm is believed to originate from S(Cys) ~ Cu(I1) ligand-to-metal charge-transfer transition. Raman spectroscopic evidence suggests that Cu-N bonds must also be present (Herve et al., 1981). Raman bands near 350-400 cm- I are assigned to Cu-N bond vibration for stellacyanin, ceruloplasmin, and laccase (Siiman et al., 1974). The band at 1640-1660 cm- I is assigned to C=O vibration involving Cu attached to the N atom of a peptide bond such as O-Cu

II

0----- Cu

I

or

- C - N-

II

I

- C - N-

The possibility of

o II -C-O-Cu is excluded, as a Cu-Gly-Gly complex gives a band at 1590 cm- I . Low-frequency Raman bands of ceruloplasmin at 415, 402, 382, 360, and 340 cm- I are assigned to the Cu-ligand stretching mode (Table 13.1). After .,j

Copper in Biological Systems

373

addition of azide and SCN- , the Cu(II)-ligand bonds of one of the two copper sites are disrupted, and the bands at 415,382, and 340 cm- I disappear. This suggests that the two copper atoms are not equivalent (Tosi et aI., 1975). There is no question that low-frequency bands arise from metal-ligand bond vibrations, but their exact assignments are difficult. Using CU-D-penicillamine as a model compound, it was assumed that the 375- and 427-cm- 1 bands originate from Cu-S stretching vibrations, and the 480-cm- 1 band is due to Cu-N vibration (Siiman and Carey, 1980). In addition to nitrogen-atom ligands, participation of cysteine-SH as a ligand in some blue copper proteins (stellacyanin, laccase, plastocyanin, ascorbate oxidase, and ceruloplasmin) is a possibility. The band near 260 cm -I in the blue copper proteins was assigned to the Cu-S vibrational mode by Siiman et aI. (1976). This assignment is reasonable. The 274-cm- 1 band of a model compound, Cu(II)NiSR), where SR is p-nitrobenzenethiolate or O-ethylcysteinate, is assigned to the Cu-S bond (Thompson et aI., 1977). However, instead of the cysteinyl (SH) group, methionine sulfur is proposed as a copper-binding site in blue copper proteins, (Ferris et aI., 1978). In the case of stellacyanin, which contains no methionine, a Cu-S (S from the disulfide bond) bond is suggested. There are also many vibrational bands in the 300-400 cm- 1 region for blue copper proteins. Judging from model compounds, some of these bands are suspected to be due to Fe(III)-S(Cys) and Fe-O stretching vibrational modes (Siiman and Carey, 1980). The Cu-N bond vibrations give intense bands near 415 and 380 cm -I. Moreover, weakly enhanced vibrational modes due to the amide are observed. They concluded that the "blue" copper site has a distorted fourcoordinated structure arising from the binding of copper to one cysteine sulfur

TABLE 13.1. Resonance Raman Frequencies of Blue Copper Proteins and Cu(II)- Sulfur Complexes in the CuN and CuS (mercaptide) Stretching and Ligand Bending Regions (Cm-').

Frequency and Assignment a

Compounds Ceruloplasmin I a Ceruloplasmin I b Azurin Azurin Tree laccase Plastocyanin Plastocyanin Stellacyanin CU(D-Pen) Cuddtc2 Assignments

422m 425m 434s 426s 420sh 425m

415m 415s 412s 419 415w

360m 374m 372m 383s 382s 379s

407s 408s 407w 408sh

388s 393w

Mostly CuN stretch

as: strong; m: medium; w: weak; sh: shoulder. Source:

and Garnier (1979).

340w

380m 402s

360w

350m 371s 367s CuS stretch

340sh 331w

337w 325w 312w Bending

The table was reproduced from Tosi

TABLE 13.2.

Frequency of Metal- Ligand Vibrations of Different Metalloproteins

Biological Molecule

MetalLigand

Wave Number (em-I)

Adrenodoxin Ferredoxin Hemerythrin

Fe-S Fe-S Fe-S Fe-O

279,350,397 345, 360 444 510

Nitrogenase Protocatechuate 3,4-dioxygenase Rubredoxin Ascorbate oxidase

Fe-S Fe-O

368 371,423,465

Fe-S Cu-S Cu-N Cu-N Cu-S Cu-N Cu-O

311, 365 260 380,415 350-400 375,427 480 282

N-Cu-N bending

119

Ceruloplasmin Copper- D- Penicillamine Hemocyanin

Alcohol dehydrogenase

Cu-N Cu-S Cu-N Cu-S Cu-N Cu-S Cu-N Cu-N Cu-O Zn-O

170-180 217-226 262-271 282-288 282 308-315 332-337 226,267 260 380,415 260 380,415 260 350-400 350 470 368

Acid phosphatase Selenocystine

Mn-S Se-Se

370 286-288

Cu-N

Cu-N Cu-N

Laccase Plastocyanin Stellacyanin Azurin

374

Reference Tang et al. (1975) Tanget al. (1975) Freier et al. (1979) Dunn et al. (1973, 1975) Freier et al. (1980) Levchenko et aI. (1980) Bull et aI. (1979) Long and Loehr (1970) Siiman et al. (1976) Siiman et aI. (1974) Siiman and Carey (1980) Siiman and Carey (1980) Loehr et aI. (1974) Freedman et al. (1976) Chen et al. (1979) Eickman et aI. (1978) Eickman et al. (1978) Eickman et al. (1978) Eickman et al. (1978) Eickman et aI. (1978) Larrabee et aI. (1977) Eickman et al. (1978) Eickman et al. (1978) Larrabee and Spiro (1980) Siiman et aI. (1976) Siiman et al. (1976) . Siiman et al. (1976) Siiman et aI. (1976) Siiman et aI. (1976) Siiman et al. (1974) Miskowski et al. (1975) Miskowski et al. (1975) Jagodzinski and Peticolas (1981 ) Sugiura et al. (1981) Lopez et al. (1981)

Copper in Biological Systems

375

and three nitrogen atoms, at least one of which is an amide nitrogen (Siiman et al., 1976). Rhus vermicifera laccase contains all three types of copper sites (types I, 2, and 3). The laccase without type 2 was prepared and called T2D (a type 2 depleted). The type 3 copper site in T2D laccase is reduced but can be oxidized by the addition of excess hydrogen peroxide. The oxidized T2D laccase gives a Raman spectrum similar to that of native laccase but not the reduced T2D. This experiment shows that the type 3 copper in T2D is in a reduced state (LuBien et al., 1981). Transferrin is an iron-containing protein (see Chapter II). Transferrin binds to Cu(II) to form a stable complex that shows an intense visible absorption band. When Cu(II)-transferrin is examined, the high-frequency region (6001700 cm -I) of the Raman spectrum has the same features as that of Fe(III)transferrin. The low-frequency region, by contrast, is more like that in the spectra of ceruloplasmin, stellacyanin, and laccase (Siiman et al., 1974). As to the binding site, it is concluded that Cu(II) binds to the phenol oxygen of tyrosine just as Fe(lII) chelates to the tyrosine residue in Fe(III)-transferrin (Tomimatsu et al., 1976; Gaber et al., 1974). The frequencies of various metal-ligand bond vibrations have been identified by many investigators. The Fe-ligand vibrations in heme compounds are summarized in Table 12.2, and Cu-N and Cu-S vibrational frequencies in ceruloplasmin and related compounds are summarized in Table 13.1. Frequencies of metal-ligand bond vibrations of many other compounds are summarized in Table 13.2. Azurins are a group of blue copper proteins found in bacteria. Azurin from Pseudomonas aeruginosa has a molecular weight of about 16,000. Copper(II) can be replaced with Ni(II), and both show resonance Raman spectra. Analysis of these spectra indicates both copper and nickel ions possessing cysteine and histidine as ligands (Ferris et al., 1979). 1.3.

Cu-PEPTIDE COMPLEX

The resonance Raman technique is useful in determining the site of the copper-peptide complex. For instance, Cu(II) forms a complex with poly(L-Tyr, L-Lys)n with an absorption maximum at 400 nm. Thus the resonance Raman spectrum can be obtained using the 457.9-nm Ar-ion laser line, which is still within the contour of the absorption band. There are two types of Cu(II)poly(L-Tyr, L-Lys) complexes. The first one occurs at pH 7.8, involving two amino nitrogens and two peptide nitrogens as ligands. The second complex is formed at alkaline pH and is coordinated with four peptide nitrogens (Tosi and Garnier, 1978; Garnier and Tosi, 1979). Normally, Cu(II) does not coordinate with the tyrosine phenolate oxygen atom, although it does coordinate with the peptide nitrogen. However, Cu(II) chelates to the phenolate oxygen atom in poly(Lys-Tyr) (Pastor et al., 1979). Glycylglycine complexes with Cu(II), but the site of attachment depends on pH. Using DC_, 15N_, and 2H-substituted dipeptides, the site of complexing

376

Copper and Other Metals in Biological Systems

and the exact assignment of some vibrational bands have been made (Takahashi et al., 1978). 2.

OTHER METALS

Many metal ions complex with a great variety of compounds. Usually they attach to specific molecular sites. Vibrational spectroscopy frequently can detect such complexing sites, since metal ions influence the vibrational modes of the functional groups to which they are attached. On some occasions, metal-ligand bonds can be detected and usually appear at relatively low frequency, because metal ions are greater in mass. Cyclic peptides are of great interest from a conformational viewpoint. Because of their cyclic nature, the conformation is less flexible than that of linear oligopeptides. The cyclo(L-Pro-GIY)3-expressed as C(PG)3-has interesting specific-cation-binding properties. It binds Li(I) and Na(I) selectively over K(I) and Rb(I). It also forms complexes of different stoichiometry with Mg(II), which binds selectively over Ba(II) and Ca(II). Upon cation complexation, the prolylcarbonyl stretching bands sharpen and upshift to 1690-1700 cm - I. The glycyl carbonyl stretching band is unaffected by Na(I), upshifted 15 cm - I by K(I), and downshifted to 1619 cm - I by Ca(III) complexation (Asher et al., 1980). Some peptides such as nonactin, monactin, and dinactin bi,nd to Na(l), K(I), Rb(I), Cs(l), Tl(l), and ammonium ions. When the peptides complex with a cation, the characteristic Raman spectra change, especially the ester carbonyl stretching frequencies (Asher et al., 1974, 1977). Histidine residues often serve as ligands in metalloenzymes such as carboxypeptidase, thermolysin, and carbonic anhydrase. Cobalt atom is frequently used as a substitute for the zinc atom in zinc enzymes. All zinc enzymes are colorless, but the substituted cobalt enzyme possesses a color that can be studied spectrophotometrically. For this reason, it is worthwhile to investigate the properties of the cobalt-imidazole complex. Unfortunately, the intensity of the resonance Raman bands of the Co(II)-;-imidazole complex are very weak. This is due to the absence of much involvement of the ligand orbitals in the visible transitions, which are largely forbidden d-d bands, and to the high energy of the ligand-cobalt charge-transfer states. Co(II)-carbonic anhydrase and Co(II)-carboxypeptidase show a very weak resonance Raman effect (Derry, 1974). Therefore, cobalt-substituted proteins have relatively limited use for resonance Raman study (Yoshida et al., 1975). Histidine forms a complex with Ni(III), Cu(II) or Zn(II) in a 2-to-l ratio, that is, (L-Hish-metal. Raman spectroscopic studies indicate that the site of coordination is the N-3 position (Itabashi and Itoh, 1980a, b). Ruthenium red inhibits calcium transport across mitochondrial membranes. It binds to various proteins, phospholipids, chelating agents, and mitochondria. Ruthenium red is used as a cytological reagent and has the structure [(NH3)5Ru-0-Ru(NH3)4-0-Ru(NH3)5]6+ . It seems that ruthenium red interacts with these biological materials in a rather specific fashion. Resonance

£!.

References

377

Raman spectra of free ruthenium red and ruthenium red complexed with Ca(II)-binding agents are quite different. Addition of Ca(II) can reverse these spectral changes. Moreover, Raman spectra of ruthenium phospholipids are different, enabling us to distinguish two classes of molecules (Friedman et aI., 1979). Ruthenium red is photosensitive; therefore, caution should be used in its use. Actually, photodegradation products can be detected from its resonance Raman spectrum (Itabashi et aI., 1981). Some enzymes such as acid phosphatase, pyruvate carboxylase, superoxide dismutase, and diamine oxidase, contain manganese as an integral part of the molecule. The resonance Raman spectrum of acid phosphatase (1230, 1298, 1508, and 1620 cm - I) shows bands very similar to the Fe(III)-transferrin and protocatechuate 3,4-dioxygenase tyrosine vibrational bands. It is concluded that Mn(III) also attaches to the tyrosine and cysteine residues of acid phosphatase (Sugiura et aI., 1980, 1981). Thiomolybdate, MoSJ- , plays and important biological role. It inhibits copper metabolism by the formation of a CuMoScprotein complex. Tetrathiomolybdate ions were detected in the hydrolysis products of nitrogenase, which is a Fe-Mo-protein complex. The Mo-S bond vibration is detected by Raman spectroscopy at 148, 158, 201, 429, 440, and 493 em-I. Copper or silver coordination to thiomolybdate influences the MoS bands by affecting Mo-S bond length (Muller et aI., 1981). Selenium belongs to the oxygen family and, although not a metal, is discussed in this chapter for convenience. As atomic weight increases from oxygen to sulfur, selenium, tellurium, and polonium, the metalloid property increases. More strictly speaking, selenium is a metalloid that is between metals and nonmetals. Selenium is a trace element and is present in a minute quantity in biological systems. It is known to be a part of the enzyme glutathione peroxidase (glutathione-H 20 2 oxidoreductase). As a first step toward the understanding of the selenium enzyme, Raman spectra of selenomethionine and selenocystine were obtained (Lopez et aI., 1981). Because of the relatively high atomic weight of selenium, the vibrations involving selenium appear at a low frequency. These are summarized in Table 13.2. Naturally occurring transferrin (see Chapter 11) contains iron, and Fe(III) can readily be replaced by Co(II) and Mn(III). Because of the similarity in the resonance Raman spectra to the natural Fe(III)-transferrin, both Co(III) and Mn(III) must occupy the same binding site as Fe(III) (Tomimatsu et aI., 1976).

REFERENCES Asher,1. M., Phillies, G. D. J., and Stanley, H. E. (1974). Nonactin and its alkali complexes-A Raman spectroscopic study. Biochem. Biophys. Res. Commun. 61, 1356. Asher,1. M., Phillies, G. D. J., Kim, B. J., and Stanley, H. E. (1977). Ion complexation in nonactin, monactin, and dinactin: A Raman spectroscopic study. Biopo/ymers 16, 157. Asher, I. M., Phillies, G. D. J., Geller, R. B., and Stanley, H. E. (1980). Cyclo(L-prolylglycyl)3 and its sodium, potassium, and calcium ion complexes: A Raman spectroscopic study. Biochemistry 19, 1805.

378

Copper and Other Metals in Biological Systems

c., Ballou, D. P., and Salmeen, I. (1979). Raman spectrum of protocatechuate dioxygenase from Pseudomonas putida; new low frequency bands. Biochem. Biophys. Res. Commrtn. 87, 836. Caughey, W. S., Barlow, C. H., Maxwell, J. c., Volpe, J. A, and Wallace, W. 1. (1975). Reactions of oxygen with hemoglobin, cytochrome c oxidase and other hemeproteins. I. Hemeproteins: Ligation phenomena. Ann. N. Y. Acad. Sci. 244, 1. Chen, J. T., Shen, S. T., Chung, C. S., Chang, H., Wang, S. M., and Li, N. C. (1979). Achatina lulica hemocyanin and its interactions with imidazole, potassium cyanide, and fluoride as studied by spectrophotometry and nuclear magnetic resonance and resonance Raman spectroscopy. Biochemistry 18, 3097. Derry, R. E. (1974). Characterization of zinc containing metalloproteins by resonance Raman spectroscopy. Master's thesis, Portland State University, Portland, Ore. Dunn, J. B. R., Shriver, D. F., and Klotz, I. M. (1973). Resonance Raman studies of the electronic state of oxygen in hemerythrin. Proc. Nat. Acad. Sci. 79,2582. Dunn, J. B. R., Shriver, D. F., and Klotz, I. M. (1975). Resonance Raman studies of hemerythrinligand complexes. Biochemistry 14, 2689. Bull,

Eickman, N. c., Solomon, E. I., Larrabee, 1. A, Spiro, T. G., and Lerch, K. (1978). Ultraviolet resonance Raman study of oxytyrosinase. Comparison with oxyhemocyanins. J. Am. Chem. Soc. 100, 6529. Evans, J. C. (1969). The peroxide-ion fundamental frequency. Chem. Commun. 682. Ferris, N. S., Woodruff, W. H., Rorabacher, D. B., Jones, T. E., and Ochrymowycz, I.. A (1978). Resonance Raman spectra of copper-sulfur complexes and the blue copper protein question. J. Am. Chem. Soc. 100, 5939. Ferris, N. S., Woodruff, W. H., Tennent, D. L., and McMillin, D. R. (1979). Native azurin and its nickel(lI) derivative: A resonance Raman study. Biochem. Biophys. Res. Commun. 88,288. Freedman, T. B., Loehr, 1. S., and Loehr, T. M. (1976). A resonance Raman study of the copper protein, hemocyanin. New evidence for the structure of the oxygen-binding site. J. Am. Chem. Soc. 98, 2809. Freier, S. M., Duff, I.. 1.., Van Duyne, R. P., and Klotz, 1. M. (1979). Resonance Raman studies and structure of a sulfide complex of methemerythrin. Biochemistry 24, 5372. Freier, S. M., Duff, I.. 1.., Shriver, D. F., and Klotz, I. M. (1980). Resonance Raman spectroscopy of iron-oxygen vibrations in hemerythrin. Arch. Biochem. Biophys. 205, 449. Friedman, 1. M., Rousseau, D. 1.., Navon, G., Rosenfeld, S., Glynn, P., and Lyons, K. B. (1979). Ruthenium red as a resonance Raman probe of Ca2+ binding sites in biological materials. Arch. Biochem. Biophys. 193, 14. Gaber, B. P., Miskowski, V., and Spiro, T. G. (1974). Resonance Raman scattering from iron(III)and copper(II)-transferrin and an iron(III) model compound. A spectroscopic interpretation of the transferrin binding site. J. Am. Chem. Soc. 96, 6868. Garnier, A, and Tosi, I.. (1979). Cupric complexes of poly(L-lysine, L-tyrosine): Spectroscopic determination of structure in aqueous solution. J. lnorg. Biochem. 10, 147. Gielens, c., Maes, G., Zeegers-Huyskens, T., and Lontie, R. (1980). Raman resonance studies of functional fragments of helix pomatia .Bc-haemocyanin. J. lnorg. Biochem. 13, 41. Herve, M., Garnier, A, Tosi, 1.., and Steinbuch, M. (1981). Spectroscopic and photoreduction studies of copper chromophores in ceruloplasmin. Eur. J. Biochem. 116, 177. ltabashi, M., and ltoh, K. (1980a). Raman scattering study on coordination structures of Cu(Il)-L-histidine( 1: 2) in aqueous solutions. Bull. Chem. Soc. Japan 53, 3131. ltabashi, M., and ltoh, K. (I 980b). Tautomerism of imidazole group and its coordination site structure in metal complexes: Raman scattering study. In Proc. Vllth Int. Conf. Raman Spectrosc., W. F. Murphy, Ed., North-Holland, Amsterdam and New York, pp. 610-611. ltabashi, M., Shoji, K., and ltoh, K. (1981). Reinvestigation of resonance Raman spectrum of Ruthenium red and its photodegradation. Chem. Lett. 491.

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Jagodzinski, P. W., and Peticolas, W. L. (1981). Resonance enhanced Raman identification of the zinc-oxygen bond in a horse liver alcohol dehydrogenase-nicotinamide adenine dinucleotidcaldehyde transient chemical intermediate. J. Am. Chern. Soc. 103,234. Larrabee, 1. A, and Spiro, T. G. (1980). Structural studies of the hemocyanin active site. 2. Resonance Raman spectroscopy. J. Am. ChenL Soc. 102,4217. Larrabee, 1. A, Spiro, T. G., Ferris, N. S., Woodruff, W. H., Maltese, W. A, and Kerr, M. S. (1977). Resonance Raman stndy of mollusc and arthropod hemocyanins using ultraviolet excitation: Copper environment and subunit inhomogeneity. J. A m. Chern. Soc. 99, 1979. Levchenko, L. A, Poschupkina, O. S., Sadkov, A P., Marakushev, S. A, Mikhailov, G. M., and Borod'ko, Yu. G. (1980). Spectroscopic investigation of FeMo-COFACTOR. Coenzyme A as one of the probable components of an active site of nitrogenase. Biochem. Biophys. Res. Commun. 96, 1384. Loehr, J. S., Freedman, T. B., and Loehr, T. M. (1974). Oxygen binding to hemocyanin: A resonance Raman spectroscopic study. Biochem. Biophys. Res. Commllll. 56, 510. Lontie, R. and Gielens, C. (1979). MIII/uscan and Arthropodan Haemocyanins. Metal/oproteins, U. Weser, Ed., Thieme, Stuttgart. Long, II, T. V., and Loehr, T. M. (1970). The possible determination of iron coordination in nonheme iron proteins using laser-Raman spectroscopy. Rubredoxin. J. Am. Chern. Soc. 92, 6384. Lopez, L., Jao, T. C., and Rudzinski, W. E. (1981). Tbe Raman spectra of selenomethionine and selenocystine. J. Inorg. Biochem. 14, 177. LuBien, C. D., Winkler, M. E., Thamann, T. J., Scott, R. A, Co, M. S., Hodgson, K. 0., and Solomon, E. 1. (1981). Chemical and spectroscopic properties of the binuclear copper active site in Rhus laccase: direct confirmation of a reduced binuclear type 3 copper site in type 2 depleted laccase and intramolecular coupling of the type 3 to the type I and type 2 copper sites. J. Am. Chem. Soc. 103, 7014. Miskowski, V., Tang, S. P. W., Spiro, T. G., Shapiro, E., and Moss, T. H. (1975). Copper coordination group in blue copper proteins. Evidence from resonance Raman spectra. Biochemistry 14, 1244. Mori, W., Suzuki, S., Kimura, M., Sugiura, Y., and Nakahara, A (1980). Characterization of the purple hemocyanin of Septioteuthis lessoniana. J. lnorg. Biochem. 13, 89. Miiller, A, Filgueira, R. R., Jaegermann, W., and Che, S. (1981). Resonance Raman spectroscopic identification of coordinating Mosl- in systems of bioinorganic interest. Natumissenschalten 68,93. Nakahara, A, Mori, W., and Suzuki, S. (1980). The active site of Septoteuthis lessoniana hemocyanin. Adv. Chern. Ser. 191, 341. Pastor, 1. M., Gamier, A, and Tosi, L. (1979). Absorption, circular dichroism and resonance Raman spectra of Cu(lI)-poly(L-glutamic, L-tyrosine) complexes. Evidence of phenolate coordination. Inorg. Chim. Acta 37, L549. Suman, 0., and Carey, P. R. (1980). Resonance Raman spectra of some ferric and cupric thiolate complexes. J. Inorg. Chem. 12, 353. Siiman, 0., Young, N. M., and Carey, P. R. (1974). Resonance Raman studies of "blue" copper proteins. J. Am. Chern. Soc. 96, 5583. Siiman, 0., Young, N. M., and Carey, P. R. (1976). Resonance Raman spectra of "blue" copper proteins and the nature of their copper sites. J. Am. Chem. Soc. 98, 744. Sugiura, Y, Kawabe, H., Tanaka, H. (1980). New manganese(III)-containing acid phosphatase. Evidence for an intense charge-transfer band and tyrosine phenolate coordination. J. Am. Chern. Soc. 102,6581. Sugiura, Y., Kawabe, H., Tanaka, H., Fujimoto, S., and Obara, A (1981). Purification, enzymic properties, and active site environment of a novel manganese(lIl)-containing acid phosphatase. J. Bioi. Chern. 256, 10664.

380

Copper and Other Metals In Biological Systems

Szymanski, T., Cape, T. W., Van Duyne, R. P., and Basolo, F. (1979). Determination of the resolution 0-0 stretching frequency of a monomeric dioxygen cobalt complex by resonance Raman spectroscopy. J. Chem. Soc., Chern. Commun. 5. Takahashi, S., Miyazawa, T, and Tasumi, M. (1978). Vibrational spectra of 13C_, 15N_ and D (C)-enriched glycylglycines and their Cu(II) complexes in aqueous solutions. Indian J. Pure Appl. Phys. 16,412. Tang, S.-P. W., Spiro, T G., Antanaitis, C, Moss, T B., Holm, R. H., Herskovitz, T, and Mortensen, L. E. (1975). Resonance Raman spectroscopic evidence for structural variation among bacterial ferredoxin, HiPIP, and Fe4S4(SCH2Ph)~- . Biochem. Biophys. Res. Commun. 62, I. Thamann, T 1., Loehr, J. S., and Loehr, T M. (1977). Resonance Raman study of oxyhemocyanin with unsymmetrically labeled oxygen. J. Am. Chem. Soc. 99,4187. Thompson,1. S., Marks, T 1., and (bers,1. A (1977). Blue copper proteins: synthesis, spectra, and structures of Cu I N 3(SR) and Cu II N 3(SR) active site analogues. Proc. Nat. Acad. Sci. USA 74, 3114. Tomimatsu, Y, Kint, S., and Scherer, 1. R. (1976). Resonance Raman spectra of iron(III), copper(II), cobalt(III) and manganese(III)-transferrin and of bis(2, 4, 6-trichlorophenolato)diimidazolecopper(II) monohydrate, a possible model of copper(II) binding to transferrins. Biochemistry 15, 4918. Tosi, L., and Gamier, A (1978). The formation and structure of a Cu(II)-poly(L-lysine, L-tyrosine) complex. Absorption and resonance spectral evidence of phenolate coordination. Inorg. Chim. Acta 29, L261. Tosi, L., and Garnier, A (1979). Circular dichroism and resonance Raman spectra of the Cu(II)-Cu(I) complex of D-penicillamine. The Cu(Cys) stretching mode in blue copper proteins. Biochem. Biophys. Res. Commun. 91, 1273. Tosi, L., Garnier, A, Herve, M., and Steinbuch, M. (1975). Ceruloplasmin-anion interaction-a resonance Raman spectroscopic study. Biochem. Biophys. Res. Commun. 65, 100. Yoshida, eM., Freedman, T. B., and Loehr, T. M. (1975). Resonance Raman study of cobalt(II)-irnidazole complexes as models for metalloproteins. J. Am. Chem. Soc. 97, 1028.

..J

CHAPTER

Al

-----mJr

Photosynthetic Pigments and Vitamin 8 12 Photosynthesis is a direct conversion of light energy into chemical energy by the chlorophyll-mediated synthesis of ATP in green plants, and by certain algae and bacteria. Chlorophyll is not the only compound involved in the energy-transfer process. It is well known that accessory pigments such as carotenoids and phycobilins are somehow involved in the photoreaction. They also serve as receptors of light energy. In photosynthetic organisms, photosynthetic reactions take place at specialized sites called reaction centers. How chlorophylls, carotenoids, quinones, and nonheme iron atoms within the reaction center are arranged and function is still unclear and is a matter of considerable interest. Using various excitation wavelengths, resonance Raman spectra of the pigments involved in photosynthesis can be obtained. The arrangement within the cell of these compounds is not random, and the

382

Photosynthetic Pigments and Vitamin 8 12

relative spatial arrangement within the cell is probably very crucial for photoenergy transfer. There have been intensive investigations in this field using resonance Raman spectroscopy. Dr. M. Lutz and his associates are contributing significantly in this area.

1.

PHOTOSYNTHETIC PIGMENTS

Chlorophylls a and b are green pigments that are structurally very similar. The difference is that one of the -CH 3 groups is replaced by a -CHO group in chlorophyll b. Electrons are delocalized over a large part of the macroring (Figure 14.1). 1.1.

RAMAN-BAND ASSIGNMENT

Chlorophylls show complex Raman bands from 200 to 1800 cm- '. The bands above 800 cm- I arise mainly from tetrapyrrolic-macrocyde vibrations. Aggregation of the chlorophylls induces characteristic spectral changes in the lowfrequency regions (100-700 cm- I ), and these low-frequency bands involve Mg-pyrrole-ligand vibrations.

C2 HS

H

H

H 3C CH2 H

I

CH2

I

C02C20H39

FIGURE 14.1. Structure of chlorophyll b. The structure of chlorophyll a is the same, except that it has a methyl group at position 3, where chlorophyll b has a formyl group.

TABLE 14.1. Resonance Raman frequencies d (cm- 1) observed in the carbonyl-stretching region for Chi a and for Chi b in chlorophyll-protein complexes at 30 K

Chloroplasts (mean values) ChI a O ChI bb 441.6 c 465.8 c 1616

1618 1630 1640

Tobacco CPU 465.8

441.6

1615sh 1634m I642sh

1615sh 1631m 1639wsh

1653 1661

CPI 441.6

Spinach CPI 441.6

Phormidium luridum CPI 441.6

Anabaena cylindrica CPI 441.6

Euglena gracilis CPI 441.6

1614m

1616m

1615m

1615m

1659w

1616m I630vwsh 1642vw 1653vwsh 1664w

I654vwsh I664wsh

1654vwsh 1664w

I654vwsh I662wsh

1656vwsh 1664vwsh

1670w 1679w 1688w

1673w 1680w 1691vwsh

1674w 1681wsh I690wsh

1674w 1680w

~ 1673w 1681w I690vwsh

1673wsh 1683w

~

~

1661w 1670 1681 1689 1694

I694w

1702

1705vwsh 1700vwsh

1705wsh

1705vwsh 1702wsh

1704vwsh Source: Table reproduced from Lutz et al. (1979). aFrom seven species. bFrom four species (Lutz 1975, 1977 and Lutz et al., 1979). c441.6, 465.8: excitation wavelength. d m: medium relative intensity, w: weak, v: very, sh: shoulder. Ca-C m are methine bridges.

1703vwsh

Assignments Phorbin, JI(Ca:":"':C m ) ChI b, JI(3-C=O) ChI b, JI(3-C=O) ChI a, JI(9-C=O) ChI a, JI(9-C=O) ChI b, JI(3-C=O) ChI a, JI(9-C=O) ChI, a, JI(9-C=O) ChI a, JI(9-C=O) ChI b, JI(9-C=O) ChI a, JI(9-C=O) ChI b, JI(3-C=O)

384

Photosynthetic Pigments and Vitamin 8 '2

Chlorophyll a contains two ester carbonyls and one keto carbonyl group; chlorophyll b contains one additional aldehyde carbonyl group. Although the 9-keto carbonyl of chlorophylls a and b and the 3-formyl carbonyl of chlorophyll b are shown in Raman spectra, no Raman activity is seen for ester carbonyl groups, because they lack conjugation with the phorbin-ring 1T-electron system. Within living cells, chlorophylls coexist ~ith proteins as. complexes (CP). In chloroplasts, or CP complexes, the C=O stretching vibrations appear in the 1620-1750-cm- I region, and most are downshifted from the free C=O stretching frequencies, but the carbonyl vibration has multiple bands and their analysis is not a simple matter. Resolution of carbonyl bands increases when the samples are cooled to 35 K. The 1630- and 1640-cm- I bands of the 35 K spectra are assigned to the aldehyde-carbonyl stretching mode of ChI b. The 1695-cm- 1 band is assigned to the free 9-ketone carbonyls of Chi b. For Chi a, the C(9)=O stretching modes appear in the 1650-1705 cm - I region (Lutz, 1975). Different carbonyl vibration bands and their assignments are shown in Table 14.1. Multiplicity of carbonyl bands in both chlorophylls a and b suggests that the group is probably involved in complex binding with proteins under natural conditions. In addition to the C(9)=O keto carbonyl group of chlorophyll a, the 1560-, 1585-, and 1617-cm- 1 bands originate from C:'::':C stretching modes of the parent ring without any noticeable participation from nitrogen motion (Lutz et aI., 1975). The low-frequency bands at 308-318 cm- I arise from the Mg-N bond in chlorophyll a, and are sensitive to the number of ligands bound to the magnesium ion (Lutz, 1974, 1975; Lutz et aI., 1975). For chlorophyll band CP IIa, the 312-cm- 1 band is assigned to Mg:..:..:.:N vibrations of the pentacoordinated-type binding to a single external ligand. The 304-cm- I component is for the hexacoordinated type. However, out-of-parent ring-plane Mg-axial-1igand bonds are unlikely to give rise to resonance-enhanced Raman bands in chlorophyll spectra. One piece of evidence is that the monomeric ch10rophyllacetone complex does not give a 31 O-cm- I band. In the complex, the carbony1s of two acetone molecules coordinate with the magnesium from each side of the phorbin plane (Lutz, 1974, 1975). There are additional low-frequency bands (100-300 cm- I ) for chlorophylls a and b and chloroplasts, but these bands have not been assigned (Lutz, 1972). There is an extensive review on the assignment of bands for free chlorophylls a and b and the pigments in chloroplasts (Lutz, 1977).

1.2.

PLANT PHOTOSYNTHETIC SYSTEM

The chloroplast is the site of photosynthesis in plants and photosynthetic eucaryotic organisms and contains large quantities of chlorophylls a and b. It also contains carotenoids. For procaryotes such as blue-green algae and the purple and green bacteria, the photoenergy-trapping process takes place in

Photosynthetic Pigments

385

chromatophores. Absorption peaks of these three pigments appear at different wavelengths; therefore, selective resonance-enhanced Raman bands can be obtained for each compound in its native environment by varying the excitation frequency. Below 450 nm the chlorophyll a Raman spectrum can be obtained; 450-475 nm is used for chlorophyll b, and wavelengths above 475 nm are used for the carotenoids (Lutz and Breton, 1973). P-700 is a pigment that undergoes bleaching when the cell is illuminated. It consists of chlorophyll a and a specific type of protein. P-700 constitutes only a small fraction (1 : 400 ratio) of the total chlorophyll in chloroplasts, and it may be considered a special form of chlorophyll a. There are two major complexes of CPo CP I is the P-700 ChI a-protein complex, whereas CP II is the CW alb-protein complex. These complexes probably represent the native states of chlorophyll. Raman spectra of chlorophyll in chlorophyll-protein complexes, intact cells, and cWoroplasts are nearly identical. This indicates that the protein-chlorophyll binding sites are probably the same in the intact membranes as in the CP complexes (Lutz et al., I978b, 1979; Pashchenko et al., 1980). What parts of chlorophyll molecules are involved in intermolecular associations is a matter of great importance. Several forms of chlorophyll a (ChI 66z , Ch1 668 , Ch1 675 , Ch1 651 , Ch1 686 , Ch1 693 ) are formed as a result of pigment-protein interaction of the C(9) = 0 keto group of the cWorophyll a molecule. On the other hand, other forms of chlorophylls such as Chl 700 and Chl 7lO are formed by molecular aggregation (Gadzhiev et al., 1981).

1.3.

BACTERIAL PHOTOSYNTHETIC SYSTEM

There are differences in the schemes of green plants, algae, and bacteria. Bacteria tend to use HzS, Na Z SZ0 3, succinate, acetate, and other organic compounds as hydrogen donors instead of HzO. Thus bacterial photosynthesis does not produce Oz. Instead of being located in the well-defined chloroplasts found in higher plants, bacterial cWorophyll is located in particles attached to lamellar extensions of the plasma membrane. In photosynthesis, transfer of excitation energy, separation of charge, and transfer of electrons take place very rapidly. These processes occur through ordered arrangements of photosynthetic molecules in membranes. An isolated photochemical reaction center can be prepared from bacterial chromophores. The isolation of such a photochemical reaction center greatly facilitates the study of the photoreaction mechanism of bacterial photosynthesis. The reaction center of Rhodopseudomonas spheroides contains four molecules of bacteriochlorophyll and two molecules of bacteriopheophytin (a derivative of chlorophyll) bound in an undetermined manner to a protein. By excitation with 600- and 529-nm laser light, resonance Raman spectra of bacteriochlorophyll or bacteriopheophytin can be selectively obtained. When the spectrum of the reaction center of R. spheroides is compared with those of isolated components, many Raman bands differ markedly in both frequency

386

Photosynthetic Pigments and Vitamin 8 12

and relative intensity. This suggests that these molecules interact with each other in the reaction center (Lutz and Kleo, 1976). Chlorophyll molecules must interact with the surrounding molecules in a specially oriented manner in the membrane. Even the aggregated chlorophyll molecules have Raman spectra different from that of the monomer, suggesting that aggregation takes place through interactions of the acetyl or keto carbonyl group of one molecule with the magnesium atom of another (Cotton and Van Duyne, 1981). In the first step of the photochemical reaction, an excited chlorophyll donates an electron to an acceptor to form a chlorophyll radical, normally cluster-expressed as ChI + '. Therefore, it is important to determine the chemical nature of the chlorophyll cation. When the spectrum of the bacteriochlorophyll a cation is compared with that of the parent molecule, significant differences in both band frequencies and intensities are found (Cotton and Van Duyne, 1978; Cotton et a1., 1980). Many Raman bands in the region of 1300-1700 cm-\ are shifted to lower frequencies. These are due to the delocalized C"-"-C stretching and bending motions of the pyrrolic ring. From this it can be said that the positive charge of the bacterial Chl+ cation becomes conjugated with part of the dihydrophorbin ring, resulting in a weakening of C=-C bonds, including the methine Ca=-Cm bridges, but C=-N and Mg-N bonds remain unaffected (Kleo and Lutz, 1978; Lutz and KIeo, 1979). One technique used to examine the photosynthetic system is to control the temperature-dependent intensity of Stokes Raman scattering by chlorophyll b and carotenoids. As the temperature is increased from 4.2 K, the shape and intensity of the spectral bands of pigments in green monocellular algae (Chlorella pyrenoidosa) change at 230 and 261 K. Finally, the spectrum becomes the spectral curve of living cells. Spectra obtained in this way represent a collective structural change of all pigments and other compounds (Drissler and MacFarlane, 1978; Drissler, 1980). 1.4.

CAROTENOIDS IN PHOTOSYNTHESIS

Carotenoids are discussed in Chapter 9, and in this section only their relationship to photosynthesis is discussed. Why carotenoids are present in the photosynthetic apparatus is not clear. Possible reasons may be that they are used in energy transfer within the photosynthetic apparatus, they protect cWorophylls from oxidation, or they are essential for structural integrity. Carotenoids can be found in chloroplasts together with chlorophylls a and b; the Raman spectra of carotenoids in the natural environment within chloro~ plasts can be obtained. Analysis indicates that four different molecular species of carotenoids are contributing to the spectrum (Lutz and Breton, 1973). There is evidence that carotenoids are also present as an integral part of the complex in the photochemical reaction center in certain photosynthetic purple bacteria (A thiorhodaceae). Resonance Raman spectra of these carotenoids are quite different from those of membrane-bound carotenoids (Lutz and Agalidis, 1978). Carotenoids found in the photochemical reaction center of photosynthetic bacteria are spheroidenes, and most spheroidenes in nature possess an

Vitamin 8 12

387

all-trans conformation. Unusual Raman spectra of the spheroidene present in the preparation of reaction centers is interpreted to mean that this compound is present in a di-cis conformation. Cis-spheroidenes are unstable and isomerize to the all-trans forms upon extraction from the reaction center. If the extraction is done rapidly in subdued light, followed by immediate freezing, the Raman spectrum shows features of the native form. This demonstrates that spheroidenes are in a cis conformation in the native photochemical reaction centers (Lutz et al., 1978a, b; Agalidis et al., 1980). Actually the reaction center of bacterial photosynthesis is quite complicated and contains not only chlorophylls and carotenoids but also bacteriopheophytins, phycocyanin, quinones, and nonheme iron. Using different excitation wavelengths, respective resonance Raman spectra can be selectively produced (Kubota et al., 1981). Raman spectra of various reaction-center-bound chromophores can be obtained from preparations of R. spheroides and other Athiorhodaceae. For instance, resonance Raman spectra of carotenoids, bacteriopheophyrins, and bacteriochlorophylls can be obtained by using the excitation wavelengths of 441.6, 528-535 and 545-550, and 580-610 nm, respectively. How these compounds are arranged in the photochemical reaction center of bacteria is a matter of great importance. Unfortunately, we still don't know the details, except that these compounds are bound to polypeptides at specific sites (Lutz, 1980a, b). Phycocyanin is an auxiliary pigment of the blue-green algae and transfers the absorbed energy via allophycocyanin to the photosystem II reaction center. The resonance Raman band of the C=C stretching vibration (1525 cm -I) of carotenoids in intact Anacystis nidulans is very sensitive to 625-nm light. Carotenoids do not absorb at this wavelength; therefore, the change in the resonance Raman spectrum cannot be due to the carotenoids themselves. The change is explained as being due to a specific phycocyanin-carotenoid interaction in A. nidulans, and the interaction probably involves the 'IT-electron system of both compounds (Szalontai and Van de Ven, 1981). Excited triple states of chlorophylls and polyenes have been recognized in the photosynthetic system, although nothing is known about the role of these triple states in photosynthesis. For the first step toward understanding this problem, resonance Raman spectroscopy was used to study the excited triple states of chlorophyll a, J3-carotene, and canthaxanthin. The results suggest that the relaxed triple conformations of all-trans-J3-carotene and canthaxanthin are different (Jensen and Wilbrandt, 1980). The Raman spectra of all-trans-J3-carotene indicate that the C=C bond order is decreased, and that the molecule may be substantially twisted probably at the C(15)=C(15') bond in the triple state (Jensen, 1980; Jensen and Wilbrandt, 1980).

2.

VITAMIN 8 12

Vitamin B12 , also called cyanocobalamin, was first isolated in 1948 and is essential in the human diet (Figure 14.2). Vitamin B12 has strong absorption bands in the near uv (340-390 om) and the visible regions (440-540 nm),

388

Photosynthetic Pigments and Vitamin B 12

C=N

Vitamin B12

FIGURE 14.2.

Structure of vitamin B I2 (cyanocobalamin).

which originate from 'TT-'TT* electronic transitions. Resonance Raman spectra of cyanocobalamin can be obtained by laser excitation coincident in wavelength with the visible absorption maxima. Dicyanocobinamide, which ::8 considerably different chemically, gives essentially identical spectra (Mayer et al., 1973a). This is reasonable, since the resonance Raman spectra are due to the resonance-enhanced vibrations associated with the common corrin ring system (George and Mendelsohn, 1973). However, an alteration in the corrin-ring chromophor induces large changes in the Raman spectra (Mayer et al., 1973b). Another possible reason for different spectra by changing the corrin-ring structure is the nonplanar nature of the corrinoid nucleus. The corrinoid ring occurs in several different forms depending on the nature of the metal and substituents. Conformational differences are largely responsible for different resonance spectra of aquocobalamin (vitamin B1u ) and cobalamin-Co(l) (vitamin B I2s )' No bands can be assigned to the vibration of the sixth ligand such as Co-C or C :::::: N. Even the in-plane Co-N stretching mode is not observed in the cobalamin spectra (Wozniak and Spiro, 1973). When a ring-stretching vibration at the 1504 cm - 1 scattering line is used, the concentration of vitamin B12 can be measured at values as low as 10- 6 M, with results reproducible within 2%. The intensity of this line is pH dependent. The change at pH 3 is due to deprotonation of benzimidazole and formation of the cobalt-ligand bond. The inflection at pH 8 corresponds to deprotonation of the coordinated water molecule (Tsai and Morris, 1975). The relative intensity of Raman bands depends on the excitation wavelength. The 1500-cm - I band of cobalt corrinoids is enhanced by visible-light excitation, whereas the 1550-cm -1 band is enhanced by UV-light excitation. This is because the electronic-transition mechanisms differ for visible light and

References 3

5

389

7

8

10

12

18 17

15

13

FIGURE 14.3. The nucleus of the cobalt corrinoid is composed of a 'IT-electron system.

UV absorption (Mayer et aI., 1973c; Salama and Spiro, 1977). As can be seen in Figure 14.3, the corrin 'IT-system is not symmetrical. Vibration along one axis (X) and along another axis (Y) should give different types of Raman spectra; these different vibrational modes may eventually appear as different Raman band patterns when irradiated with laser light of different wavelengths.

REFERENCES Agalidis, 1., Lutz, M., and Reiss-Husson, F. (1980). Binding of carotenoids on reaction centers from Rhodopseudomonas sphaeroides R 26. Biochim. Biophys. Acta 589, 264. Cotton, T. M., and Van Duyne, R. P. (1978). Resonance Raman spectroelectrochemistry of bacteriochlorophyll and bacteriochlorophyll cation radical. Biochem. Biophys. Res. Commun. 82,424. Cotton, T. M., and Van Duyne, R. P. (1981). Characterization of bacteriochlorophyll interactions in vitro by resonance Raman spectroscopy. J. Am. Chem. Soc. 103, 6020. Cotton, T. M., Parks, K. D., and Van Duyne, R. P. (1980). Resonance Raman spectra of bacteriochlorophyll and its electrogenerated cation radical. Excitation of the Soret bands by use of stimulated Raman scattering from Hz and D z . J. Am. Chem. Soc. 102,6399. Drissler, F. (1980). Discovery of phase transitions in photosynthetic systems. Phys. Lett. 77A, 207. Drissler, F., and MacFarlane, R. M. (1978). Enhanced anti-Stokes Raman scattering from living cells of Chlorella pyrenoidosa. Phys. Lett. 69A, 65. Gadzhiev, Z. I., Godzhaev, N. M., Gorokhov, V. v., Churin, A. A., Pashchenko, V. Z., and Rubin, L. B. (1981). Study of certain features of intermolecular interactions of chlorophyll a in vivo by resonance Raman spectroscopy. Dokl. Akad. Nauk. SSSR 261, 497. George, W.O., and Mendelsohn, R. (1973). Resonance Raman spectrum of cyanocobalamin (vitamin BIZ)' Appl. Spectrosc. 27, 390. Jensen, N. H. (1980). Photosynthetic Pigments and Model Compounds Studied by Pulse Radiolysis, Risj", ""."", 'M

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Longitudinal Sections

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° ° °0 ° ° ° (b)

(e)

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FIGURE 15.7. Diagram of normal muscle.

bundles corresponds to the length of the A band (Figure 15.7). When contraction takes place, the actin filaments slide toward the M band, and the light I band disappears. 4.1.

MYOSIN

Myosin is the major component of muscle and accounts for half of the myofibrillar protein. Myosin has a large size, with a molecular weight of

Muscle

actin only

403

myosin and actin

FIGURE 15.8. Ultrastructure of normal muscle-cross sectional view. The large dot is myosin; the small dot, actin (electron micrograph by M. Stringer of the author's laboratory).

480,000. The amide I band appears at 1650 cm- I , which indicates the presence of a-helical conformation. The amide III band also shows that the protein has typical a-helical conformation, and appears at 1265 and 1304 cm -I. Myosin also contains nonhelical structure, as indicated by the band at 1244 cm- I . The 1244-cm - I band represents either ,a-structure, random coil, or a mixture of both (Carew et al., 1975). The conformation of myosin can be influenced by some cations, and the transition can be detected using amide I and III bands, and bands at 900 and 940 cm- I • For instance, CaCl 2 transforms myosin from a-to ,a-structure, and LiBr denatures the protein, thus increasing the random-coil structure (Barrett et al., 1978). 4.2.

MYOSIN SUBFRAGMENTS

Light meromyosin (LMM) and subfragment I, S-I, are characteristic of the helical-tail and globular-head portions of the myosin molecule. The LMM consists of two a-helical chains wound into a rodlike shape, somewhat similar to a supercoil. The S-I contains about 35% ,a-structure, as measured by optical rotary dispersion. Raman spectra of LMM and S-I seem to reflect these structural differences in the amide III region. The LMM lacks bands in the

404

Eyes, Teeth, and Muscles

l244-l265-cm - 1 region, whereas the S-l has a band in the l240-l280-cm - 1 region. The LMM also has a band near 1306 cm- I , whereas the S-l does not. The l306-cm -1 band probably represents the coiled helices of the fibrous tail portion, whereas the 1265-cm- I band is associated with a-helical portions of the globular heads (Asher et a1., 1976). 4.3.

TROPOMYOSIN AND TROPONIN

Both tropomyosin and troponin, components of skeletal muscle, regulate the interaction of actin and myosin. Tropomyosin has the amide I band at 1655 cm -1, the amide III band at 1254 cm -1, and the band at 940 cm - 1. Judging from these bands, tropomyosin has mainly a-helical structure. The a-content, however, decreases rapidly as the pH is raised above 9.5 (Frushour and Koenig, 1974). Nadeau et a1. (1982) showed that the amide I band is centered at 1646 cm -1. Troponin C is the Ca(II)-binding subunit of troponin. Addition of Ca(II) ion to troponin C produces perturbation in the amide III region, showing evidence for increased a-helical content (Carew et a1., 1980). 4.4.

WHOLE MUSCLE

As can be seen from Figure 15.9, the Raman spectrum of whole muscle is strikingly similar to that of myosin. This is reasonable, as myosin is the major component and accounts for approximately 50% of muscle proteins (Asher et a1., 1976). An examination of the Raman spectrum of intact single muscle fibers indicates that some proteins are bound to intracellular-membrane fi-carotene. Carotenoid pigments are known to give strong resonance Raman bands at 1530 and 1160 cm- I that originate from -C=C- and =C-C= stretching vibrations of the conjugated polyene chains. Indeed, strong bands at 1521 and 1156 em- 1 are clearly visible in the Raman spectrum' of a single muscle fiber (Pezolet et a1., 1978a, b). The amide I at 1648 em - I and a strong skeletal C-C stretching band at 939 em-I also indicate that muscle fiber contains large amounts of a-helix proteins. However, a-helix content decreases when the myofibrils are isolated. Apparently the state of myofibrils in situ is different from that of myofibrils outside intact muscle tissue (Pezolet et al., 1980b). When the O-H stretching vibration bands (3100-3700 em-I) of an intact single muscle fiber are examined, there is no appreciable difference between the shape and relative intensity of the bands due to the water molecules located inside the muscle fiber and the shape and intensity of the corresponding bands in the spectrum of pure water. This suggests that there is little specially structured intracellular water. Since ice and liquid water have different Raman spectra in the OH vibrational region, it is possible to examine frozen and unfrozen water in a frozen intact muscle cell. By this method it is found that about 20% of the water molecules remain in the supercooled state at - 5°C.

References

405

-f:j.v(cm) FIGURE 15.9. Raman spectra of myosin (a, b) and whole muscle (c). The figure was reproduced [rom Asher et al. (1976) by permission of copyright owner, Raven Press.

which corresponds to I g of water per gram of fiber dry weight. This amount of water is probably truly the "bound water" (Pezolet et al., I978a, b). This value is somewhat larger than that found with the calorimetric method (Aubin et al., 1980). These studies suggest that a constant amount of water is bound to the protein molecules, and that this amount does not vary with water content of the muscle. 4.5.

CONTRACTILE STATE AND PROTEIN STRUCTURE

Because good-quality Raman spectra can be obtained from a single intact muscle fiber, the Raman spectroscopic technique can be used to correlate the protein structure to the state of muscle contraction. This was beautifully done by Pezolet et al. (1980a). A predominantly a-helical structure of muscle proteins remained even when the muscle was contracted or relaxed in the presence of ATP and Ca(II). However, the contraction induced a decrease in the scattering intensity of some of the Raman bands that are due to the acidic and tryptophan residues, showing that these amino acids are involved in the generation of tension.

REFERENCES Asher, l. M., Carew, E. B., and Stanley, H. E. (1976). Laser Raman spectroscopy: A new probe of the molecular conformations of intact muscle and its components. In Physiology of Smooth Muscle, E. Bulbring and M. F. Shuba, Eds., Raven. New York. DO. 229-238.

406

Eyes, Teeth, and Muscles

Askren, C. c., Yu, N.-T., and Kuck, Jr., 1. F. R. (1979). Variation of the concentration of sulfhydryl along tbe visual axis of aging lenses by laser Raman optical dissection technique. Exp. Eye Res. 29, 647. Aubin, M., Prud'Homme, R. E., Pezolet, M., and Caille, J.-P. (1980). Calorimetric study of water in muscle tissue. Biochim. Biophys. Acta 631, 90. Barrett, T. W., Peticolas, W. L., and Robson, R. M. (1978). Laser Raman light-scattering observations of conformational changes in myosin induced by inorganic salts. Biophys. J. 23, 349. Carew, E. B., Asher, 1. M., and Stanley, H. E. (1975). Laser Raman spectroscopy-new probe of myosin substructure. Science 188, 933. Carew, E. B., Leavis, P. c., Stanley, H. E., and Gergely, J. (1980). A laser Raman spectroscopic study of Ca2+ binding to troponin c. Biophys. J. 30, 351. East, E. 1., Cbang, R. C. c., and Yu, N.-T. (1978). Raman spectroscopic measurement of total sulfhydryl in intact lens as affected by aging and ultraviolet irradiation. J. BioI. Chern. 253, 1436. Frushour, B. G., and Koenig, 1. L. (1974). Raman spectroscopic study of tropomyosin denaturation. Biopolymers 13, 1809. Goheen, S. c., Lis, L. J., and Kauffman, 1. W. (1978). Raman spectroscopy of intact feline corneal collagen. Biochim. Biophys. Acta 536, 197. Kuck, Jr., 1. F. R., East, E. 1., and Yu, N.-T. (1976). Prevalence of a-helical form in avian lens proteins. Exp. Eye Res. 23, 9. Mathies, R., and Yu, N.-T. (1978). Raman spectroscopy with intensified vidicon detectors: A study of intact bovine lens proteins. J. Raman Spectrosc. 7, 349. McKenzie, C. R. (1979). Raman and infrared studies of biologically relevant systems: The ocular lens and glutathione. Diss. Abstr. Int. B. 39, 4707. Nadeau, J., Pezolet, M., Williams, D. L., Jr., and Swenson, C. A. (1982). Personal communication. Nishigori, K, Yamada, M.-O., Fujimori, K, Chikamori, K, and Yamashita, S. (1979). Comparative studies on fish tooth tissues by micronuorometry and Raman-spectroscopy. In Acta Histochern. Cytochem., 20th meeting, JSHC, Kyoto, Part I, p. 599. Pezolet, M., Pigeon-Gosselin, M., and Caille, 1.-P. (1978a). Laser Raman investigation of intact single fibers protein conformations. Biochim. Biophys. Acta 533, 263. Pezolet, M., Pigeon-Gosselin, M., Savoie, R., and Caille, 1.-P. (1978b). Laser Raman investigation of intact single muscle fibers on the state of water in muscle tissue. Biochirn. Biophys. Acta 544,394. Pezolet, M., Pigeon-Gosselin, M., Nadeau, J., and Caille, 1.-P. (1980a). A molecular probe of tbe contractile state of intact single muscle fibers. Biophys. J. 31, I. • Pezolet, M., Pigeon-Gosselin, M., Nadeau, J., and Caille, 1.-P. (1980b). Laser Raman scattering as a probe of muscle structure. In Proc. Vllth Int. Conf. Raman Spectrosc., W. F. Murphy, Ed., North-Holland, Amsterdam and New York, pp. 600-603. Scbachar, R. A., and Solin, S. A. (1975). The microscopic protein structure of the lens with a theory for cataract formation as determined by Raman spectroscopy of intact bovine lens. Invest. Ophthalmol. Vis. Sci. 14, 380. Thomas, D. M., and Schepler, K. L. (1980a). Raman spectra of normal and ultraviolet-induced cataractous rabbit lens. Invest. Ophthalmol. Vis. Sci. 19, 904. Thomas, D. M., and Schepler, K. L. (1980b). Laser Raman spectroscopy of ultraviolet-induced cataracts in rabbits and monkeys. Gov. Rep. Announce. Index (U.S.) 80, 4924. Also U.S. Air Force Report SAM-TR79-40, p. 1. Yamada, M.-O., Horibe, H., Fujimori, K, Yamashita, S., and Yamashita, T. (1979). Paleobiophysical studies on tooth tissues by micronuorometry and Raman-spectrometry. Cel/. Molec. Bioi. 25, 167.

~

References

407

Yu, N.-T., and East, E. 1. (1975). Laser Raman spectroscopic studies of ocular lens and its isolated protein fractions. J. Bioi. Chem., 250, 2196. Yu, N.-T., Jo, B. H., Chang, R. C. c., and Huber, 1. D. (1974). Single-crystal Raman spectra of native insulin structures of insulin fibrils, glucagon fibrils, and intact calf lens. Arch. Biochem. Biophys. 160,614. Yu, N.-T., East, E. J., and Chang, R. C. C. (1977). Raman spectra of bird and reptile lens proteins. Exp. Eye Res. 24, 321.

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CHAPTER

Raman Microprobe, MOLE

The Raman microprobe is called by different names, such as the Raman microscope, the Delhaye molecular microprobe, an optical microscope using the Raman effect, the Raman laser microprobe, or simply MOLE (molecular optical laser examiner). It is a combination of a microscope and a Raman spectrometer. MOLE was developed mainly by the efforts of three laboratories: Black Engineering, Inc.; the U.S. National Bureau of Standards; and Centre National de la Recherche Scientifique at Lille, France (Hirschfeld, 1973; Rosasco et al., 1975; Delhaye and Dharmelincourt, 1975). MOLE gives a standard microscopic image as well as a two-dimensional microscopic image of a sample at a certain shift from the exciting frequency (Raman lines). The only part of the sample that appears in the second case is the one that exhibits the Raman effect at the particular wave number under study. In this way heterogeneous samples can be differentiated under the microscope. Also, the Raman spectrum of a sample from a narrowly focused area can be obtained. From the spectrum we can determine the type of compound present in that particular area. MOLE provides the composition of the sample at the molecular level

412

Raman Microprobe, MOLE

usually without damaging. Unlike an electron microscope, which must be operated under high vacuum, the MOLE gives an image using almost any condition, such as the presence of water, air, or at high temperatures. MOLE is used for the qualitative and quantitative localization on a microscopic scale of organic, inorganic, and biological samples. One advantage of MOLE is that it allows visualizing a very small area of the sample, down to 1 X 1 !-tm in size. This is useful to identify the nature of a compound in a tiny spot in a gem or crystal or to see and identify the nature of a pollutant. In a sample with a homogeneous surface, the Raman spectrum obtained from a small area represents the spectrum of the sample's overall area. For instance, the spectrum of a unit 1 !-tm in length of calf thymus DNA fiber obtained by MOLE is identical to the spectrum obtained by a conventional method from a much larger area of the sample (Adar, 1978). It is well known that a laser is a relatively high-energy beam. So it is important to determine whether heating effects on samples may cause problems. Investigation indicates that heating effects become less severe as the particle size decreases (Etz and Blaha, 1980). However, sample sensitivity to the tightly focused, hence very intense, laser beam sets a practical upper limit on incident laser power (about 100-150 mW). There have been some technical improvements in MOLE recently. For instance, the attachment of a multichannel optical detector shortens the time required for obtaining a Raman spectrum, and this also avoids excess heat absorption by samples (Etz, 1980; Etz et al., 1980). There are excellent review articles by Rosasco (1980) and by Adar (1981) on the basic theory as well as applications.

1.

THEORY

The basic principle of the Raman microprobe is somewhat similar to that of the electron microprobe (Figure 16.1). In the electron microprobe, an electron beam is focused in vacuum on the surface of a solid sample. By analyzing the scattered secondary electrons and emitted characteristic X rays, one can determine the position and the concentration of a given element on the surface. In the Raman microprobe, photons (light) are used, and from the scattered Raman light one can detect and identify the compounds and their structures (Delhaye and Dhamelincourt, 1975; Dhamelincourt et al., 1979). MOLE consists of two components; one is a microscope (imaging system) and the other is a Raman spectrometer (spectral mode) (Figure 16.2). From the Raman spectrometer component of MOLE we can get a Raman spectrum, from which we can identify the nature of a compound. The sample is illuminated by a laser (vo ) beam, and the sample emits Rayleigh-scattered (vo ) and Raman-scattered light (vo ± vI' Vo ± V 2 " ' " Vo ± vn ). The frequencies vI ... vn are characteristic of the molecular vibrations of a molecule. The total image of the sample can be obtained in the microscope when Vo is used. This image is the same as that seen with a conventional

...

Theory

413

Excitations

Electrons

Backscattered or secondary electrons Fluorescence X-rays

Electron Microprobe

hv o hv Rayleigh o + h{v l - vol Raman

Raman Microprobe

FIGURE 16.1. The basic principle of the Raman microprobe and an electron microprobe. There is an analogy between these two probes.

microscope. But with the microscope in MOLE, the light can be filtered to give "n" If the sample is observed through MOLE with the frequency of "0 - "n' one sees the image of the p~ion of the sample that gives the Raman-scattered light. However, the frequency one selects to reconstruct the image must be well above the background. All other parts of the sample are not seen under this condition (Figure 16.3). The overall appearance of MOLE is shown in Figure 16.4. "0 -

mlcr05COpe con~rol

optical

fil~er

cra-~recorder

'screen

Raman

spectrometer

FIGURE 16.2. A simplified diagram of a Raman microprobe. The figure was reproduced from Ballan-Dufranpis et aI. (1979) by permission of the copyright owner. Biologie Cellulaire.

414

Raman Microprobe, MOLE

>-.

Raman spectrum of substance A

~

OM ~

ctl

I'l

CIl ~

~

ctl~ ~

p::

'M

14,1---=--¥'j!\

II

I I .-/

!\

Vcm-1

"0

c~ ~ ~ ~,

--y--

Image

Raman spectrum of substance B Raman spectrum '~ubstance C

V

~

/

Image obtained using a particular Raman line

FIGURE 16.3. A diagram showing why MOLE can show the localization of a particular constituent in a heterogeneous sample. The figure was reproduced from Dhamelincourt and Bisson (1977).

FIGURE 16.4. An overall view of MOLE. The photograph was kindly supplied by Dr. M. Delhaye and Dr. 1. Oswalt, Jobin-Yvon Instruments, France.

2.

CLINICAL AND HISTOLOGICAL APPLICATIONS

The Raman microprobe is useful for the in situ analysis of cellular inclusions. Several examples are shown in this section. The foreign material within a lymph node from a patient with a silicone elastomer finger-joint prosthesis was detected by MOLE (Abraham and Etz,

Clinical and Histological Applications

415

1979). The light micrograph of the lymph node shows the foreign material within multinucleated giant cells (Figure 16.5). The Raman spectra of the microscopic foreign inclusion in the lymph node and of the prosthesis are identical (Figure 16.6). The foreign material inside a histological section of fish liver was identified by MOLE as disordered graphite carbon (Delhaye et al., 1979). Purine compounds in tissue can be detected by MOLE. As a result of nucleic acid and protein degradation, certain purine compounds such as uric acid, guanine, and xanthine accumulate in cells and tissues. In situ study of such bioaccumulated compounds has been difficult because of the lack of specific histochemical reagents for purines. Moreover, their chemical structures are similar, so exact identification has been difficult. By the use of MOLE, uric acid, guanine, or xanthine have been identified in spider cuticle, fish skin, Blatella fat granule, and other animal tissues (Ballan-Dufran9ais et al., 1979) (Figures 16.7 and 16.8). The formation of stones (renal lithiasis) in different parts of the urinary system is a common disease for persons of all ages. How the stone is formed is not known, but it is widely believed that it is due to a metabolic abnormality. Kidney stones can be made of inorganic salts such as calcium phosphate or calcium carbonate, or they can be organic stones such as cysteine stone, oxalate stone, or uric acid stone. The chief constituent of a kidney stone is calcium. Identification of kidney-stone composition is important, so a physician can advise a patient what dietary course should prevent another kidney stone from forming. MOLE not only can locate the kidney stone in the nephron, but it can also determine its composition. For instance, for one type of stone, the Raman

FIGURE J6.5. A section of lymph node with foreign bodies of silicone rubber within multinucleated giant ceIls. The arrow indicates typical inclusions of silicone polymer. The star shows the cytoplasmic area analyzed to obtain the micro-Raman spectrum of the host tissue matrix. The figure was reproduced from Abraham and Etz (1979) by permission of the American Association for the Advancement of Science. The photograph was kindly supplied by Drs. Abraham and Etz.

416

Raman Microprobe, MOLE

)

(a)

I)

CYTOPLASM OF GIANT CELL

~

0.1.

I

I

I

2

u

>f-

FOREIGN BODY IN GIANT CELL

(a)

IL

3000

I,

~

I

I"lj I 0

~ f~

I

0

SILICONE ELASTOMER

2000

1000

o

RAMAN SHIFT (em-I)

FIGURE 16.6. Spectra recorded in the Raman probe microanalysis of a deparaffinized standard 5-JLtn section of lymph node. The figure was reproduced from Abraham and Etz (1979) by copyright permission of the American Association for the Advancement of Science. The photograph was kindly supplied by Drs. Abraham and Etz.

spectrum shows three distinct bands at 1075, 970, and 278 cm - I. The 1078-cm- 1 band corresponds to the carbonate C-O vibrational mode and the 970-cm- 1 band to the symmetrical P-O vibration, and the 278-cm- 1 band indicates the presence of calcite CaC03 . Therefore, the kidney stone is made up of calcium phosphate and calcium carbonate. Mineralizations in kidneys of rabbits intoxicated by HgC1 2 , periwinkle concretions, and conjunctive cells were also studied by MOLE (Truchet et al., 1980). There are two types of oxalate stones: calcium oxalate monohydrate and calcium oxalate dihydrate. These two types of crystals can be readily distinguished by MOLE. The monohydrate shows a Raman line at 1462 cm- I, and the dihydrate shows a line at 1476 cm- I . Likewise, cysteine stone can be readily detected by the characteristic vibrational band of S-S stretching at 499 cm- I. Other types of kidney stones such as uric, calcium phosphate, and calcium carbonate stones can also be detected by their characteristic Raman lines. Thus MOLE is a powerful tool in the analysis of calculi (Daudon et al., 1980). Myxomycetes are mushrooms that secrete mineralized grains whose chemical identity was previously unknown. Using MOLE, the grains were found to .J

FIGURE 16.7. (A) Histological section of spider (X680). C, cuticle; E, epithelium; G, guanine concretions; 0, approximate analyzed area. (B) Histological section of fish (XSOO). S, skin; G, needles of guanine; 0, approximate analyzed area. The photograph was reproduced from BallanDufran~ais et al. (1979) by permission of the copyright owner, Biologie Cellulaire.

418

Raman Microprobe, MOLE

a

b

c 500

1000

1500

.b.\lcm 1

FIGURE 16.8. Raman spectra obtained from MOLE. (A) Spider guanophore. (8) Standard guanine. (C) Fish guanophore. Note the striking similarities in the spectra. These results demonstrate that the concretions seen in the micrograph are pure guanine. The spectra were reproduced from Ballan-Dufran~s et aI. (1979) by permission of the copyright owner, Biologie Cellulaire.

be composed of calcite, since they show the characteristic Raman lines at 1090, 715, and 280 em-I (Locquin and laeschke-Boyer, 1980). Enamel formation is common in animal tissues. Enamel formation is characterized by the nucleation of a mineral deposit and its growth during the secretory stage of ameloblasts. Fully grown extracellular enamel eventually becomes 99% mineral in the tissue. The vibrational analysis of hydroxylapatite permits the detection of enamel in the rat incisor (Casciani and Etz, 1979). Examination of mollusk tissue shows a very distinct band at 474 em - I that is an indication of the S-S stretching vibration. This is due to the presence of CuS in intermediate compounds degraded from hemocyanin, which is a copper-sulfur compound (Ballan-Dufranljais et al., 1979). Pyrocystis lunula is a dinoflagellated algae that emits light. The substance responsible for light emission has not yet been identified. Using MOLE, the

Environmental Applications

419

FIGURE 16.9. The image was obtained using one of the resonance Raman lines of carotenoids at 1527 cm - I. Localization of carotenoids in carrot-root cell. The photograph was kindly supplied by Dr. M. Delhaye. The source of the photograph is P. Bisson, These de 3eme cycle, Universite de Lille, Juillet 1977.

location of bioluminescent materials within the cells have been identified. Judging from the Raman spectrum, the compound may be luciferin (Arrio et aI., 1980). Localization of carotenoids (see Chapter 14, Section 1.4) in a cell of a carrot root is shown in Figure 16.9. Carotenoids are polyene compounds that give resonance Raman spectra. Using one of the carotenoid resonance Raman lines, one can obtain an image of the carotenoid localization. The same kind of Raman image can easily be obtained from a variety of living cells, including both plants and algae (Cavagnat et aI., 1981).

3.

ENVIRONMENTAL APPLICATIONS

Wide use of pesticides causes considerable environmental problems. Many pesticides are absorbed by cattle, fish, and humans, and these pesticides usually become embedded in the tissues. Identification of the absorbed pesticides is an important, yet difficult, problem. Interferential contrast microscopy shows the pesticide location; only the Raman microprobe allows their identification without extraction (Delhaye et aI., 1979; Arrio et aI., 1980). Many ciliated protozoans ingest nutrients and inert, insoluble pollutants by endocytosis. The important question is whether ingested pesticides are metabolized or remain intact. Raman microprobe investigations indicate the pesticides 4,4'-dichlorodiphenyl and j3-endosulfan remain intact, with no chemical modification occurring in the cells (Dive et aI., 1980a, b). Some polynuclear aromatic hydrocarbons are potent carcinogens. Such compounds are often found in polluted urban air produced by photochemical reactions of miscellaneous hydrocarbons released to the air after combustion of

420

Raman Microprobe, MOLE

fossil fuels. Pyrene and phenanthrene are detected in airborne particles as small as 30 !tm (Etz, 1979).

4.

OTHER APPLICATIONS

MOLE is also applied to paleontology. Both calcite and argonite are calcium carbonate, but they have different crystal forms. Thus they have slightly different carbonate vibration bands. When MOLE was us~d, the calcite nature of protozoan Ammonia beccarii was found to be calcareous lamellae and that of Hoeglundina elegans, aragnonitic in nature (Venec-Peyre and Jaeschke-Boyer, 1978).

REFERENCES Abraham, J. L., and Etz, E. S. (1979). Molecular microanalysis of pathological specimens in situ with a laser-Raman microprobe. Science 206, 716. Adar, F. (1978). Use of the molecular microprobe to record Raman spectra of a single mitochondrion and a fiber of calf thymus DNA. Fron. BioI. Energ. 1, 592. Adar, F. (1981). Developments in Raman microanalysis. In Microbeam Analysis, H. Geiss, Ed., San Francisco Press, San Francisco, pp. 67-72. Arrio, B., Dupaix, A., Fresneau, C., Lecuyer, B., and Volfin, P. (1980). Etudes spectroscopiques in vivo de cellules vegeiales bioluminescentes: Pyrocystis lunula. L'Actualite Chimique 4, 18.

c., Truchet, M., and Dhamelincourt P. (1979). Interest of Raman laser microprobe (mole) for the identification of purinic concretions in histological sections. BioI. Cellulaire 36, 51.

Ballan-Dufran~s,

Casciani, F. S., and Etz, E. S. (1979). Raman microprobe study of biological mineralization in situ: Enamel of the rat incisor. In Microbeam Analysis, Dale E. Newbury, Ed., San Francisco Press, San Francisco, pp. 169-172. Cavagnat, R., Cruege, F., and Pham, V. H. (1981). Biological applications of resonance Raman spectroscopy and resonance micro-Raman spectroscopy. Biochimie 63, 927. Daudon, M., Jaeschke-Boyer, H., Protat, M. F., and Reveillaud, R. J. (1980). La microsonde Mole et l'analyse des calculs urinaires. Perspectives et realites. L'Actualite Chimique 4,25. Delhaye, M., and Dhamelincourt, P. (1975). Raman microprobe and microscope with laser excitation. J. Raman Spectrosc. 3, 33. Delhaye, M., Dhamelincourt, P., and Wallart, F. (1979). Analysis of particulates by Raman microprobe. Toxicol. Environm. Chem. Rev. 3, 73. Dhamelincourt, P., and Bisson, P. (1977). Principle and realization of an optical microscope using the Raman effect. Microsc. Acta 79, 267. Dhamelincourt, P., Wallart, F., Leclercq, M., N'Guyen, A. T., and Landon, D. O. (1979). Laser Raman molecular microprobe (MOLE). Anal. Chem. 51, 414A. Dive, D., Devynck, J. M., Leroy, G., Coustaut, D., and Moschetto, Y. (1980a). Principles and examples of applications of the Raman microprobe in the biological area. L'Actual. Chimique 4,24. Dive, D., Devynck, J. M., Leroy, G., Fourmaux, M. N., and Moschetto, Y. (1980b). Identification of intracellular particles of pesticides in ciliate protozoa by Raman microprobe. Experientia 36,832.

References

421

Etz, E. S. (1979). Raman microprobe analysis: principles and applications. In Scanning Electron Microscopy, SEM, AMF O'Hare, IIl., pp. 67-92. Etz, E. S. (1980). New Raman microprobe with multichannel optical detector. In National Bureau of Standards Dimensions 11, I. Etz, E. S., and Blaha, 1. J. (1980). Scope and limitations of single particle analysis by Raman microprobe spectroscopy. In Proc. Spec. Sess. on Particle Anal., 13th Ann. Conf. Microbeam Anal. Soc., Ann Arbor, Michigan, pp. 153-197. Etz, E. S., Adar, F., Landon, D.O., and Steinbach, W. R. (1980). A new Raman microprobe with multichannel optical detector-characteristics and applications. In Proc. 10th N. E. Regional ACS Mtg. Abstract, Potsdam, N.Y. Hirschfeld, T. (1973). Raman microprobe: vibrational spectroscopy in the Femtogram range. Opt. Soc. Am. 63, 476. Locquin, M., and Jaeschke-Boyer, H. (1980). Structure calcitique inframicroscopique de grains de secretion microniques chez les myxomycetes. L 'Actual. Chimique 4, 22. Rosasco, G. J. (1980). Raman microprobe spectroscopy. In Advances ill Infrared and Raman Spectroscopy, Vol. 7, R. J. H. Clark and R. H. Hester, Eds., Heyden, London, pp. 223-282. Rosasco, G. J., Etz, E. S., and Cassatt, W. A. (1975). The analysis of discrete fine particles by Raman spectroscopy. Appl. Spectrosc. 29, 396. Truchet, M., Martoja, M., Martoja, R., and Ballan-Dufran~s,C. (1980). Applications de la mole a l'mineraux sur coupes histologiques. L'Actual. Chimique, p. 15. Venec-Peyre, M.-T., and Jaeschke-Boyer, H. (1978). Micropaleontologie. Application de la microsonde moleculaire illaser Mole a l'etude du test du quelques Foraminiferes calcaires. C. R. Acad. Sc. 287, 607.

CHAPTER

Clinical and Environmental Applications

CLINICAL DIAGNOSIS: TISSUES AND CELLS

le application of Raman spectroscopy to clinical problems is still in its infant 1ge, but it has a great future potential. In recent years, the Raman spectra of blood have proved to be sensitive to rious pathological disturbances affecting human blood plasma, and this ~thod of diagnosis claimed to be superior to conventional clinical tests such the sedimentation rate of erythrocytes. In the Stokes-frequency range )00-4000 cm -I), the overall spectra and fluorescence backgrounds of blood lsma taken from patients suffering mammary carcinoma and pseudolcinous papillary cystodeno carcinoma were shown to differ considerably m the spectra of normal blood plasma (Larsson and Hellgren, 1974). In jition, the low-frequency Raman spectra (up to 200 cm - I) of human

Clinical Diagnosis: Tissues and Cells

423

mammary carcinoma and normal human mammary tissues appear to differ in that the shift lines, at given frequencies, seen with normal tissues tend to become much broader and resolved into two or three separate lines in the spectra of homologous malignant mammary tissues (Figure 17.1) (Webb et aI., 1977a). Similar alterations in the millimeter microwave spectra of tumor versus normal cells including mammary tissues also have been observed (Webb and Booth, 1971; Webb et aI., 1977b). Thus both Raman and microwave spectroscopy of blood sera and tissues may become diagnostic tools for the rapid detection of mammary carcinoma as well as other malignant diseases (Webb, 1976; Webb and Lee, 1977; Webb, 1980). One of the more interesting facets of the Raman spectroscopy of intact cells is found with microbial cells. The Raman spectra of bacterial cells when they are in the resting state have been found to be essentially devoid of shift lines, whereas the spectra of growing cells display many lines of a complex nature (Webb and Stoneham, 1976a, b, 1977; Webb et aI., 1977b; Webb, 1980). In addition, at normal physiological temperatures, the spectra of algal cells show only lines assigned to carotenoid pigments; the expected lines from the large chlorophyll molecules apparently are absent and may be seen only in the spectra of such cells when they are held at temperatures below 261 K (Drissler, 1980). Such observations have led to the suggestion (Webb, 1980) that many of the shift lines seen in the spectra of active cells arise from Raman-active energy states induced in vivo by metabolic activities. This suggestion was based not only on the lack of lines from resting cells but also on the finding that the "active cell" Raman spectra were altered when growing cells were exposed to

B

A

lcm-1 J FIGURE 17.1. Raman spectra of (A) normal human mammary tissue, (B) normal right-side and (C) left side 2-3 cm mammary carcinoma of human. The figure was reproduced from Webb et al. (l977a) by permission of the copyright owner, John Wiley.

424

Clinical and Environmental Applications

microwave fields (from 40-140 GHz) during the determinations of their Raman spectra. Microwaves of such frequencies have been shown to affect the growth and metabolic activities of both bacteria (Webb and Dodds, 1968; Webb and Booth, 1969; Berteaud et al., 1975) and yeast cells (Grundler et al., 1977). It appears, therefore, that normal in vivo metabolic activities may be followed by Raman spectroscopy, and this same technique may be used to assess the influence of imposed microwaves stresses on them. It is possible, therefore, that with refinements in techniques, Raman spectroscopy may prove to be a useful tool in the assessment of the mechanisms by which the functions of the nervous and cardiovascular systems become impaired when they are exposed to microwave fields of low intensities, as has been reported in numerous publications. The infection of animal and microbial cells by viruses is known to alter metabolic processes severely, as does the physical or chemical induction of prophages and latent viruses (such as the Herpes complex) normally carried by some bacterial and animal cells, respectively. It has been found that the microwave spectra of bacterial cells carrying prophages differ in small detail from those of the same cell strain not possessing the virus (Lee and Webb, 1977). The "active" Raman spectra of these two cell types also differ, especially when the prophage in the carrier strain is induced to multiply in vivo by agents such as X rays, uv light, and chemical carcinogens (Webb, 1981). The presence, in vivo, of a carried virus or viral infection from outside apparently may be detected, therefore, by Raman spectroscopy, and such a procedure could enhance greatly the rapid clinical diagnosis and detection of viral diseases. Differences were observed in the Raman lines of a bacteria cell (Escherichia coli) suspension when illuminated by laser light of 10-400 mW for only 1 s (O'Sullivan and Santo, 1981). Raman spectroscopy may become an analytical technique to detect the state of bacteria or tissues in a metabolically active condition.

2.

CLINICAL ANALYSIS

Catecholamines (adrenaline and noradrenaline, also called epinephrine and norepinephrine) are neurotransmitters that play an important role in biological systems. With hypertension, pheochromocytoma, and other disorders, catecholamine levels in urine are elevated. Clinical analysis of adrenaline (epinephrine) and noradrenaline (norepinephrine) concentrations is important, as in some nerve disorders the levels of these compounds vary from normal values. Analysis is also important because these compounds are used as drugs for the treatment of some disorders. The normal procedure for the analysis is a fluorometric technique that requires the conversion of catecholamines to trihydroxyindoles. A variety of quenching agents and other fluorescent materials can interfere with this analysis. Resonance Raman spectroscopy can also be used to analyze for these compounds. For this analysis, catecholamines are

Environmental Problems

425

first oxidized by ferricyanamide to the corresponding aminochromes. The C=N+ stretching vibration mode of aminochromes can be resonance enhanced. Aminochromes are determined at 1480 cm -1 for adrenaline, 1425 cm- I for noradrenaline, and 1415 cm- I for dopamine (Morris, 1975, 1976; Rahaman and Morris, 1976). In order to establish Raman spectroscopy as a tool for the analysis of sympathomimetic amines, Raman spectra of amphetamine, methamphetamine, benzamphetamine, diphenhydramine, phendimetrazine, phentermine, ephedrine, and related drugs were obtained. It was concluded that these drugs can be differentiated by Raman spectroscopic techniques (Bass, 1978). Phenothiazines are drugs widely used as antipsychotics in the treatment of psychosis and can be analyzed by Raman spectroscopy due to the presence of the C-S bond (Kure and Morris, 1976). Barbiturates are drugs widely used for neuropsychiatric therapy in cases of insomnia and as sedatives and anticonvulsants. Widespread use of barbiturates has made their detection and analysis an ever-increasing problem in clinical, forensic, and toxicological laboratories. All barbituric acids contain the pyrimidine-ring structure. The strong Raman bands at 629 ± 8 cm - I (free acid) and 642 ± 4 cm ~ I (sodium salts) are due to the breathing vibrations of the pyrimidine ring. Most barbiturates are readily distinguished from each other by analysis of specific Raman band frequencies (Willis et al., 1972). Sulfonamides are well-known drugs commonly used as antibiotics. By diazotization, colorless drugs are converted to colored compounds from which resonance Raman spectra can be obtained. The detection limit is as low as 2 X 10- 8 M (Sato et al., 1980). Many drugs interact with nucleic acids. These are discussed in Section 6.4., Chapter 5. Many drugs show polymorphism in the solid state; therefore, they exist in several crystalline forms having different physical properties and different absorption rates when administered as drugs. Griseofulvin is a drug used in the treatment of fungus infections. This compound exists in the solid state in the unsolvated form and can form solvates with different solvents. The manner of its solvation (solute-solvent interaction) can be studied by Raman spectroscopy. In the benzene solvate, only weak van der Waals interactions exist between solute and solvent. However, in solvates with chloroform and bromoform, weak hydrogen bonding exists between the proton of the solvent and the keto group of the benzofuran ring in griseofulvin. When desolvation occurs, the crystal does not go through any intermediate, and the lattice reverts to the structure of unsolvated griseofulvin (Bolton and Prasad, 1981).

3.

ENVIRONMENTAL PROBLEMS

One important aspect in environmental research is to analyze pollutants quantitatively and also to identify compounds. Most compounds we would need to find in air, water, soil, and biological tissue are usually present in very

426

Clinical and Environmental Applications

small amounts. In order to identify a compound and its quantity, analytical methods must be simple, rapid, and accurate. Raman spectroscopy can be an ideal analytical tool for certain compounds. 3.1.

PESTICIDES

The detection of residual pesticides in air, soils, water, and animal tissues is an important step in environmental control. There has been considerable effort to use Raman spectroscopy for such analysis. Raman spectra of parathion, Guthion, ethion, Furadan, Baygon, Endosulfan, dieldrin, lindant, Aroclor, and 0, P' DDT [1-( O-chlorophenyl)-l-( p-chlorophenyl)-2, 2, 2-trichloroethane] were obtained by Vickers et aI. (1973). The work so far is preliminary, but it does indicate the feasibility of this technique. Raman spectra of chlorinated, sulfur-containing, phosphorus-containing and many other pesticides such as DDT, TDE, Perthane, methoxychlor, Dicofol, Terradifon, heptachlor, chlordane, dieldrin, endrin and Endosulfan, Pepulate, CDEC (2-chloroallyldiethyldithiocarbamate), thiram, maneb, zineb, ferbam, malathion, ethion, Methylparathion, parathion, EPN, O,O-diethyl0-(2, 4-dichlorophenyl)phosphorothioate, Dichlorvos, Mevinphos, tributyl phosphorotrithioite, 2, 4-dichlorobenzyltributylphosphonium chloride, IPC (isopropyl-N-phenylcarbamate, propham), CIPC (chloropropham), EPTC (ethyl-N, N-dipropyl-3-chlorophenylcarbamate), and nicotine were obtained by Nicholas et aI. (1976a, b, c). These are common pesticides currently used in agriculture in the United States. By comparing the fingerprint bands, they concluded that Raman spectroscopy is potentially useful for analysis of these pesticides. An attempt was made to detect chlorinated-hydrocarbon pesticides on thin-layer-chromatography plates by Raman spectroscopy. It was found that Raman detection requires at least 200 p,g of sample compared with a few micrograms needed for Fourier-transform IR spectroscopy (Gomez-Taylor et aI., 1976). This indicates that this application of Raman spectroscopy is potentially useful; yet it needs further refinement to be' a good analytical tool for pesticide detection. Phenylamide pesticides do not exhibit resonance Raman spectra, but when converted to azo-dye derivatives, they show good resonance Raman spectra that can be used for analysis of the pesticides (Higuchi et aI., 1980). 3.2.

FOOD ADDITIVES

The use of coloring additives in food is common practice in the food industry. The conventional methods of analyzing these dyes are tedious and time consuming; usually such analysis involves chromatographic and colorimetric methods. Dyes are suitable for analysis by resonance Raman spectroscopic methods, as each dye has its own absorption characteristic. Raman spectra of

References

427

artificial dyes FD & C Red, Nos. 2, 4, and 40 were obtained. Each dye has a unique Raman fingerprint, permitting identification of concentrations as low as 5 ppm. This result is promising, as the dye can be analyzed in situ without going through time-consuming separation steps (Brown and Lynch, 1976). The concentration of nitrate in water can be readily analyzed by Raman spectroscopy using a nitrate vibration line at 1045 cm -1. The detection limit is about 2 ppm. For waste and treated water, analysis becomes harder, due to the strong luminescence. With potassium iodide as a quencher, the sensitivity becomes comparable to that of pure water (Furuya et al., 1979).

4.

OTHERS

Bacterial spores contain about 10% dipicolinate. It is thought that this factor is responsible for the high resistance in the presence of calcium ion of spores to heat and other environmental stresses. The analysis of the carboxyl-group vibrational mode of Raman spectra indicates that the carboxyl group is not a simple calcium-salt type. From this, it was concluded that dipicolinate in the spore protoplasts is not the simple calcium salt. Calcium ion and dipicolinate are probably involved in some type of interaction, the nature of which is still unknown (Woodruff et al., 1974). Carbon monoxide is known to alter the in vivo metabolic activity of bacteria. Exposure of E. coli to carbon monoxide changes its metabolic activity and its metabolic time clock. This change can be followed by observing the l273-cm -1 Raman band. As the bacteria and CO interact, the intensity of the l273-cm -1 band decreases (Stoneham and Webb, 1976). Some bacteria contain carotenoids; thus from their resonance Raman spectra, bacteria can be differentiated. Some bacteria exhibit pronounced carotenoid overtone and combination bands (Howard et al., 1980).

REFERENCES Bass, V. C. (1978). The identification of sympathomimetic amines by Raman spectroscopy. Forens. Sci. 11, 57. Berteaud, M. A J., Dardalhon, M., Rebeyrotle, N., and Averbeck, M. D. (1975). Action d'un rayonnement electromagnetique illonguerev d'onde millimetrique sur la croissance bacterienne. C. R. Acad. Sci. 281, 843. Bolton, B. A, and Prasad, P. N. (1981). Laser Raman investigation of pharmaceutical solids: Griseofulvin and its solvates. J. Pharm. Sci. 70, 789. Brown, C. W., and Lynch, P. F. (1976). Identification of FD & C dyes by resonance Raman spectroscopy. J. Food Sci. 41, 1231. Drissler, F. (1980). Discovery of phase transitions in photosynthetic systems. Phys. Lett. 77A, 207. Furuya, N., Matsuyuki, A, Higuchi, S., and Tanaka, S. (1979). Determination of nitrate ion in waste and treated waters by laser Raman spectroscopy. Water Res. 13,371.

428

Clinical and Environmental Applications

Gomez-Taylor, M. M., Kuehl, D., and Griffiths, P. R. (1976). Vibrational spectrometry of pesticides and related materials on thin layer chromatography adsorbents. Appl. Spectrosc. 30, 447. Grundler, W., and Keilmann, F. (1978). Nonthermal effects of millimeter microwaves on yeast growth. Z. Naturforsch. 33C, 15. Grundler, W., Keilmann, F., and Frohlich, H. (1977). Resonant growth rate response of yeast cells irradiated by weak microwaves. Phys. Lett. 62A, 463. Higuchi, S., Aiko, 0., and Tanaka, S. (1980). Determination of trace amounts of some phenylamide pesticides by resonance Raman spectroscopy. Anal. Chirn. Acta 116, 1. Howard, Jr., W. F., Nelson, W. H., and Sperry, 1. F. (1980). A resonance Raman method for the rapid detection and identification of bacteria in water. Appl. Spectrosc. 34, 72. Kure, B., and Morris, M. D. (1976). Raman spectra of phenothiazine and some pharmaceutical derivatives. Talanta 23, 398. Larsson, K., and Hellgren, L. (1974). Combined Raman and fluorescence scattering from human blood plasma. Experientia 30,481. Lee, R. A, and Webb, S. J. (1977). Possible detection of in vivo viruses by fine structure millimeter microwave spectroscopy between 68 and 76 GHz. IRCS Med. Sci. 5, 222. Morris, M. D. (1975). Resonance Raman spectra of the aminochromes of some biochemically important catecholamines. Anal. Chern. 47, 2453. Morris, M. D. (1976). Determination of catecholamines by resonance Raman spectroscopy of their aminochromes. Anal. Lett. 9, 469. Nicholas, M. L., Powell, D. L., Williams, T. R., and Bromund, R. H. (I 976a). Reference Raman spectra of DDT and five structurally related pesticides and of five pesticides containing the norbomene group. J. Assoc. Offic. Anal. Chern. 59, 197. Nicholas, M. L., Powell, D. L., Williams, T. R., and Huff, S. R. (1976b). Reference Raman spectra of ten phosphorus-containing pesticides. J. Assoc. Offic. A nal. Chern. 59, 1071. Nicholas, M. L., Powell, D. L., Williams, T. R., Thompson, R. Q., and Oliver, N. H. (I 976c). Reference Raman spectra of eleven miscellaneous pesticides. J. Assoc. Offic. Anal. Chern. 59, 1266. O'Sullivan, R. A, and Santo, L. (1981). Experimental aspects in Raman spectroscopy of microorganisms. Abstr., Spec. Issue Can. J. Spectrosc., June. Rahaman, M. S., and Morris, M. D. (1976). Determination of adrenaline and noradrenaline by resonance Raman spectrometry. Talanta 23, 65. Sato, S., Higuchi, S., and Tanaka, S. (1980). Determination of small amounts of some sulfonamide drugs by resonance Raman spectroscopy. Anal. Chirn. Acta 120, 200. Stoneham, M. E., and Webb, S. J. (1976). Action of carbon monoxide on bacteria as seen by laser-Raman spectroscopy. Int. Res. Cornrnun. Sys., Med. Sci. 4, 520. Vickers, R. S., Chan, P. W., and Johnsen, R. E. (1973). Laser excited Raman and fluorescence spectra of some important pesticides. Spectrosc. Lett. 6, 131. Webb, S. 1. (1976). Nutrition Time and Motion in Metabolism and Genetics. Thomas, Springfield, Ill. Webb, S. 1. (1980). Laser-Raman spectroscopy of living cells. Phys. Repts. 60, 201. Webb, S. J. (1981). Detection and inquction of in vivo viruses as seen by laser-Raman spectroscopy. Personal communication. Webb, S. J., and Booth, AD. (1969). Absorption of microwaves by microorganisms. Nature 222, 1199.

Webb, S. J., and Booth, A D. (1971). Microwave absorption by normal and tumor cells. Science

174,72. Webb, S. 1., and Dodds, D. E. (1968). Inhibition of bacterial cell growth by 136 gc microwaves. Nature 218, 374.

References

429

Webb, S. J., and Lee, R. A. (1977). Microwave and laser-Raman spectra of normal and tumour human mammary tissue. IRCS Med. Sci. U.K. 5, 102. Webb, S. 1., and Stoneham, M. E. (1976a). The effect of microwaves on the metabolic time clocks of normal and tumour cells. A laser-Raman study. IRCS J. Med. Sci. UK 4, 10. Webb, S. 1., and Stoneham, M. E. (1976b). Action of CO on bacteria as seen by laser-Raman spectroscopy. IRCS J. Med. Sci. U.K. 4, 520. Webb, S. J., and Stoneham, M. E. (1977). Resonances between 10 II and 10 12 Hz in active bacterial cells as seen by laser Raman spectroscopy. Phys. Lett. 6OA, 267. Webb, S. J., Lee, R. A., and Stoneham, M. E. (I 977a). Possible viral involvement in human mammary carcinoma: A microwave and laser-Raman study. Int. 1. Quant. Chem.: Quallt. BioI. Symp. 4, 277. Webb, S. J., Stoneham, M. E., and Frolich, A. (1977b). Evidence for non-thermal excitation of energy levels in active biological systems. Phys. Lell. 63A, 407. Willis. Jr., J. N., Cook, R. B., and Jankow, R. (1972). Raman spectroscopy of some common barbiturates. Anal. Chern. 44, 1228. Woodruff, W. H., Spiro, T. G., Gilvarg, C. (1974). Raman spectroscopy in vivo: Evidence of the structure of dipicolinate in intact spores of Bacillus megaterium. Biochem. Biophys. Res.

Commull.58, 197.

IIII~I~I~~~EN~~~I~II

About Professor

C.V.Raman The essence of science is independent thinking, hard work and not equipment.

-G. V. Raman

I think it is appropriate to present briefly a personal history of Professor C. v. Raman, an eminent Indian physicist, whose keen mind and astute observations led to the discovery of the scattering effect that bears his name. C. V. Raman was born in Thiruvanaikkaval near Trichinopoly, southern India, on November 7, 1888, as one of seven children. He obtained his master's degree in physics from Madras University and came to Calcutta in August 1907 as an officer of the Accountant General of Bengal. His research on spectroscopy after office hours made him an honorary worker at the Indian Association for the Cultivation of Science. In July 1917, C. V. Raman was appointed Palit Professor and Head of the Department of Physics of the Calcutta University of Science (Chakravarti, 1978).

Appendix

431

During a voyage to England, Raman was struck with the idea that the deep blue color of the sea might be due to light scattering by water molecules, independent of the presence of any suspended matter. He considered that the color of the sea was fundamentally the same phenomenon as that observed in the sky, namely, the scattering of light by the molecules in the air (Raman, 1921; Ramanathan, 1978). Upon his return to India, Raman extended Lord Rayleigh's work on the scattering of light and extensively published papers on the light scattering and magnetism of liquids and solids. He published 57 papers before reporting on the effect now known as Raman scattering. The first line spectrum showing the Raman effect was made in the evening of February 28, 1928, in the laboratory of the Indian Association for the Cultivation of Science at 210 Bow Bazar Street, Calcutta. Professor Raman observed that highly purified organic liquids contained weak scattering components of frequencies not originally present in the incident light. A fascinating fact is that he observed the new radiation by eye. Raman suspected that this scattered frequency was analogous to the Compton effect. In 1923, the American physicist Arthur Holly Compton in Chicago found that the scattering of X rays by the electrons in a graphite target gave rise to a second X ray band with shifted wavelength. Raman therefore concluded that there were new types of scattered light that must be optical analogs of the Compton effect. The first announcement of the discovery of modified scattered radiation in scattering was made by Professor Raman in an inaugural lecture delivered under the title "A New Radiation," on Friday, March 16, 1928, at a meeting of the South Indian Association in Bangalore (Krishnan, 1978). The text was published in the Indian Journal of Physics, 2, 387-398 (1928). The text of the speech consisted of nine parts. They were (i) "Introduction," (ii) "A New Phenomenon," (iii) "Its Universality," (iv) "Line-Spectrum of New Radiation," (v) "Nature of the New Radiation," (vi) "Relation to Thermodynamics," (vii) "Coherent or Non-Coherent Radiation?" (viii) "Possible X-Ray Analogues," (ix) "Conclusion." Professor Raman was very confident about his finding and his first sentence was, "I propose this evening to speak to you on a new kind of radiation or light-emission from atoms and molecules." Then he explained the phenomena of fluorescence and light scattering. In "A New Phenomenon," he described the history of the investigation made in Calcutta. The first hint that he and his assistant, Mr. Seshagiri Rao, found, in December 1921, was that the depolarization of light transversely scattered by distilled water increased very markedly when a violet filter was placed in the incident-light path. Later, in 1922, using dust-free methyl and ethyl alcohol, he noticed that the colors of scattered light from the different liquids did not match. In the summer of 1923, Professor Raman and Dr. K. R. Ramanathan suspected that the difference in color was due to scattered light. Ramanathan described this as "a trace of fluorescence." Since 1923, the investigation of this "weak fluorescence" was the main effort of Professor Raman and his associates. Although the effect was called "feeble

432

Appendix

fluorescence" at the time, Professor Raman thought this was not fluorescence. In his speech he said, " ... the impression left on my mind at the time was that we had here an entirely new type of secondary radiation distinct from what is usually described as fluorescence." After Professor Compton's study of X-ray scattering, Professor Raman accelerated his light-scattering study. He used a powerful beam of sunlight from a heliostat concentrated by a 7-in. telescope objective combined with a short-focus lens. The light was passed through a blue-violet filter and then through the liquid under examination. The new type of radiation, Professor Raman observed, was not restricted to liquids. Mr. K. S. Krishnan and Professor Raman observed the same phenomenon in the gases CO2 and N 20. They noticed that the scattering power of gases was much weaker than that of liquids. It was further determined that this new type of radiation could be observed in crystals such as ice. Thus the phenomenon was observed with the three phases of matter. In his inaugural lecture in 1928, Professor Raman explained the first Raman spectra made on photographic plates. He was not satisfied by the discovery alone, but proposed to explain the theory of the new phenomenon. He clearly stated, "As a tentative explanation, we may adopt the language of the quantum theory, and say that the incident quantum of radiation is partially absorbed by the molecule, and that the unabsorbed part is scattered." He had already predicted the usefulness of Raman scattering in the study of molecular structure by saying, "The measurement of the frequencies of the new spectral lines thus opens a rleW pathway of research into molecular spectra, particularly those in the infra-red region." The prediction was emphasized again in the final part of his speech, "We are obviously only at the fringe of a fascinating new region of experimental research which promises to throw light on diverse problems relating to radiation and wave theory, X-ray optics, atomic and molecular spectra, fluorescence and scattering, thermodynamics and chemistry. It all remains to be worked out." All of these points he made in 1928. Raman recognized the importance of the scattering phenomenon and stated in his letter to the Spex Speaker that from September 1921 to February 1922, he thought" the molecular scattering of light in a transparent medium is a universal phenomenon exhibited in various degrees by all such materials, viz., crystalline solids, glasses, liquid and gases" (Raman, 1966). During the period September 1927 to February 1928, his thoughts became more specific about light scattering, and he said, "It began with my attempts to reconcile the apparent conflict between the ideas of wave-optics and Einstein's idea that light consists of discrete quanta of energy. That a reconciliation was possible between these two concepts of the nature of light was demonstrated by my success in deducing on the basis of the classical wave-principles, the existence, as well as the characteristics, of the two types of X-ray scattering, respectively with and without a change of frequency" (Raman, 1966). C. V. Raman and K. S. Krishnan submitted a paper to Nature on February 16, 1928, under the title "A New Type of Secondary Radiation." It was published in Nature, 121, 501-502 (1928). Again, on March 6, 1928, C. V.

Appendix

433

Raman submitted a one-page paper, "A Change of Wave-Length in Light Scattering," to Nature, and the article was published in volume 121, page 619, in 1928. With these announcements and publications, "a new radiation," presently known as the Raman effect, was revealed to the world. The equipment originally used by Raman consisted of a quartz mercury lamp, a container for the sample, a condensing lens, and a pocket spectroscope. Later, more-powerful mercury arcs, large-aperture spectrographs, and photographic recordings were used. In order for the photographic plate to have a good exposure, an exposure of hours and even days was given. Raman was not aware of the theory that predicted the scattering effect he observed. In 1923 an Austrian physicist, A. Smekal, published a paper predicting the frequency shift of inelastic light scattering (Andrews, 1978). Actually, there are other people who, independently, predicted the Raman effect. Rocard concluded from his research that scattered light must have a different spectral structure than incident light (Rocard, 1928). Brillouin delivered to the French Academy of Science a report that Rocard had published a note on Raman scattering in Comptes Rendues on March 23, 1928. One week later, Fabry reported to the French Academy on a note by Cabannes (1928), who predicted the Raman effect as early as 1924. Landsberg and Mandelstam at the Institute for Theoretical Physics, without knowing of Raman's publication, submitted a paper to the German journal Naturwissenschaften on the same effect Raman observed (Landsberg and Mandelstam, 1928). So the effect was predicted by several investigators before Professor Raman actually observed the effect. However, Professor Raman was the first person to publish an actual spectrum of scattered light containing shifted frequencies. Readers who are interested in the historical aspects of Raman spectroscopy are advised to read the article by BrandmUller and Kiefer (1978). The news of Raman's discovery did not evoke much interest in London at that time, because very few physicists were actively working on the problem of light scattering. Dr. R. W. Wood, an American physicist working on light scattering, immediately checked the Raman effect after reading the letter by Raman (Lord, 1978). Wood rechecked his own spectroscopic plates taken earlier and found evidence of the same effect Raman observed. He cabled his results and published them in Nature (Wood, 1928). In the beginning of his cable he stated, "PROF. RAMAN's brilliant and surprising discovery that transparent substances illuminated by very intense monochromatic light scatter radiations of modified wavelength, and that frequency of difference between emitted radiations and one exciting medium is identical with frequency of infrared absorption bands opens up wholly new fields in the study of molecular structure." At the end of the cable, he praised Professor Raman's discovery by saying, "It appears to me that this very beautiful discovery, which resulted from Raman's long and patient study of phenomena of light scattering, is one of most convincing proofs, of quantum theory of light which we have at present time."

434

Appendix

Wood introduced the new terminology of anti-Stokes scattering to the higher frequency of Raman lines (Brandmiiller and Kiefer, 1978). At the end of 1928, Wood, Rasetti, and McLennan showed that the Raman displacements actually represented the vibrational or rotational frequencies of the diatomic molecules, liquid nitrogen and oxygen (Asundi, 1978). Wood observed the Raman effect of HCI gas and obtained the Raman line at 2886.0 cm -I that coincided with 2885.9 cm -I, a value well established by its IR spectrum for this frequency and left no doubt as to its origin. The energy associated with the 2886 cm - I band actually corresponds to an energy transition from the ground state to the first excited vibrational level. In 1931, the book entitled Der Smekal-Raman Effect by K. W. F. Kohlrausch was published in Germany, and this upset Professor Raman very much. In 1938 the second edition of this book appeared, again under the same title. By this time the entire scientific community was unanimously calling this effect just the Raman effect. When the 1928 Nobel Prize in physics was awarded to Richardson, it was expected by several scientists that the 1929 prize would be awarded to Raman, but instead it was given to de Broglie, who discovered the matter wave. But in 1930 Professor Raman was rightly awarded the prize. His Nobel lecture was delivered on December 11, 1930, and consisted of nine parts (Raman, 1931). The first one was "The Color of the Sea." This shows how interested he was in the deep blue color of the sea, probably recalling his first voyage to England through the Red Sea and the Mediterranean, where he first thought of the light-scattering phenomenon. The titles of the other sections of the Nobel lecture were (ii) "The Theory of Fluctuation," (iii) "The Anisotropy of Molecules," (iv) "A New Phenomenon," (v) "The Optical Analogue of the Compton Effect," (vi) "Its Spectroscopic Character," (vii) "Interpretation of the Effect," (viii) "The Significance of the Effect," and (ix) "Some Concluding Remarks." In the concluding remarks he praised the works of Dr. McLennan on liquified gases and Dr. Wood and Dr. Rasetti on their light-scattering work. Professor Raman not only contributed to the fundamental knowledge of light scattering but also to the application of the Raman effect to practical problems. One example is the identification of diamond from its Raman spectrum (Bhagavantam, 1978). Professor Raman's last scholarly work was published in Nature in 1945, when he was 57 years old. The title was "Scattering of light in crystals," andit was his 94th paper (Raman, 1945). His first paper was entitled "The Doppler effect in the molecular scattering of radiation" and also was published in Nature (Raman, 1919). Throughout his life of 82 years, he devoted himself to the study of the phenomena of light scattering. It seems he was always absorbed in something to do with color. A student, Dr. S. Ramaseshan, wrote, "A few months before he died, I remember, while walking with him one evening amongst the eucalyptus groves that he loved, he stopped me in his characteristic manner and pointing towards the sky said: 'Have you seen

References

435

anything so beautiful?' " Till his end he was fascinated by the color of the sky, the effect of light scattering. Readers who are interested in original papers of Professor C. V. Raman are directed to the book published by the Indian Academy of Science (1978). Since the discovery of the Raman effect in 1928 and its subsequent recognition by world scientists, there has been rapid progress in this field, as can be witnessed by the 1800 scientific papers and Raman spectra on over 2500 compounds published by 1939 (Long, 1978). The total number of publications on Raman spectroscopy exceeds 23,600 up to the end of 1978 (Krishnan and Shankar, 1980). I had an occasion, in 1979, to give a seminar at the Biophysics Unit of the Indian Institute of Science in Banga10re, and was impressed by the quality of scientists at the institute. Professor Raman was the director of the Indian Institute of Science in 1933. Even based on the standards of the United States and Europe, the Indian Institute of Science is a first-class research institute. Here I observed the influence of Professor Raman, where he is still remembered and respected by scientists of the younger generation. As a scientist who works on Raman spectroscopy, the visit to Banga10re was one of the most memorable and moving events in my life. I wish he could have lived to see the tremendous development in the biological application of Raman spectroscopy. He died in 1970, about the time the biological application of Raman spectroscopy began. REFERENCES Andrews, D. (1978). The discovery of the Raman effect. New Sci. 16, March 1978,722. Asundi, R. K. (1978). Reminiscences relating to the discovery of the Raman effect. Curro Sci., 47, 192. Bhagavantam, S. (1978). The discovery of the Raman effect, reminiscences of Sir C. V. Raman. In Proc. Sixth Int. Can/. Raman Spectrosc., E. D. Schmid, R. S. Krishnan, W. Kiefer, and H. W. Schrotter (Eds.). Heyden, London, Philadelphia, Rheine, pp. 3-12. Brandmiiller, J. and Kiefer, W. (1978). Physicists' view, fifty years of Raman spectroscopy. Spex Speaker 23, 310. Chakravarti, R. N. (1978). Fifty years of Raman effect: 1928-1978. J. Inst. Chem. (India), SO, 187. Krishnan, R. S. (1978). Fifty years of Raman effect-some recent developments. Curro Sci. 47, 196. Krishnan, R. S. and Shankar, R. K. (1980). Progress of research on the Raman effect: A statistical analysis. J. Indian Inst. Sci., 62, 53. Landsberg, G. and Mandelstam, L. (1928). Eine neue Erscheinung bei der Lichtzerstreuung in Kristallen. Naturwissenschaften, 16, 772. Long, D. A. (1978). Raman spectroscopy in Europe for the past fifty years. In Proc. Sixth Int. Can/. Raman Spectrosc., E. D. Schmid, R. S. Krishnan, W. Kiefer, and H. W. Schrotter (Eds.). Heyden, London, Philadelphia, Rheine, pp. 13-27. Lord, R. C. (1978). The early days of Raman spectroscopy in the United States. In Proc. 6th Int. Can/. Raman Spectrosc., E. D. Schmid, R. S. Krishnan, W. Kiefer, and H. W. Schrotter (Eds.). Heyden, London, Philadelphia, Rheine, pp. 29-37.

436

Appendix

Raman, C. V. (1919). The Doppler effect in the molecular scattering of radiation. Nature, 103, 165. Raman, C. V. (1921). The colour of the sea. Nature, 108,367. Raman, C. V. (1928). A new radiation. Indian 1. Phys., 2, 387. Raman, C. V. (1931). The molecular scattering of light, Nobel lecture. Les Prix Nobel, en 1930. Stockholm, Imprimerie Royale, P. A. Norstedt. Raman, C. V. (1945). Scattering of light in crystals. Nature ISS, 196. Raman, C. V. (1966). Laser Raman spectroscopy. The Spex Speaker, XI, I. Ramanathan, K. R. (1978). Some reminiscences of my association with Professor Raman. Curl'. Sci. 47, 179. Rocard, Y. (1928). Les nouvelles radiations diffusees. C. R. Ac. Sci., 186, 1107. Wood, R. W. (1928). Wave-length shifts in scattered light. Nature 122, 349.

Index

A,165 Absorption band, 18.317 Absorption of light, 3-6 Absorption spectra, heme compounds, 317 2-Acetamido-2-deoxY-D--glucose, 240, 246 Acetyl group, carbohydrates, 245 N-Acetyl group, 246 N-Acetylg!ucosamine, 235-239, 245, 246 N-Acetylhistidine methylamide, 82 N-Acetylprolinamide, 80 N-Acetylserine methylamide, 82 N-Acetyltyrosine methylamide, 82 Acid anhydride, 36 Acid phosphatase, 83, 377 Acoustic accordionlike motion, 191 Acridine orange, 57 Actin, 401 Actinomycin, 163 Active Raman spectra of cells, 424 Adenine, 59. 148,150,154,155,160,184 Adenosine, 159 ADP, 162, 163,283 Adrenaline, 424 Adrenaredoxin, 307 Adrenodoxin, 309, 374 Adriamycin, 165 Airborne particles, 420 (L-Alah,82 L-Ala-L-Ala,82 Ala-Gly, 82 Albumin, 209 Alcohol dehydrogenase, 124, 127, 128,374 Aldehyde, 36, 137 Alkylation, 156, 157

Alkylmercury, 160 Allosteric effect, 349 AII-rrans-retinal, 272, 273, 275-277 Alpha-cystalline, 397 Alpha (a)-helix, 70, 72-75, 79, 80-83, 85, 98, 99,107,108,176,179,180,184,403,405 Amide, 79, 80, 137 Amide I band, 68-70, 73, 74, 76-83, 85, 97, 98, 103,108,177, 182,200,214,225,403 Amide II band, 68, 71 Amide III band, 40, 68, 70, 71, 73, 74, 76-83, 85, 86, 97, 98, 103, 108, 182, 225, 403 Amide IV band, 71, 72 Amide V band, 71, 72 Amide VI band, 71, 72 Amide VII band, 71, 72 Amide A band, 67 Amide B band, 67 4-Amidino-4'-dimethylaminoazobenzene, 127 Amine, 311 Amine oxidase, 370 D--Amino acid, 81, 82 Aminochromes, 425 2-Amino-2-deoxY-D--glucose, 240 4-Amino-3-nitro-rrans-cinnamic acid, 121 AMP, 143, 152, 159, 160, 166, 167 Amphetamine, 425 Amphipathic molecule, 188 Amphotericin B, 217, 218 Amplitude, definition, 4, 13 Amylose, 250, 251 Anisotropy, 34, 434 Antibiotic-lipid interaction, 213-218 Antibiotics, 69, 165,425 "'27

438

Index

Antibonding, 327 Antiferromagnetism, 370 Antifreeze glycoprotein, 108 Antiparallel-{3-sheet (ant iparallel-pleated sheet), 73, 75, 82,107,129 Anti-Stokes, 6-14, 55, 56, 434 Anti-Stokes Raman scattering: definition, 6, 7 origin, 8-12 Antisymmetrical molecular-scattering tensor, 347 ApA, 167 Apamin,83 ApG,136 ApU, 150 Aquocobalamin, 388 Arginine, 209 Argininylvasopressin, 93 Aroclor, 426 Aromatic hydrocarbons, 419 Ascorbate oxidase, 370, 373, 374 Aspartic acid, 300 Assignment of vibrations. rule, 27 Astaxanthin, 261 Asymmetrical ring vibrational mode, 235 Asymmetrical stretching vi brat ion, 21, 25, 27, 29,31,32,198,199,210,245,247,320 ATP, 161-163,222,223,270,283,284.40 1,405 ATPase, 223 Axial-ligand, 332-339, 341-343 Azo group, 38, 121-123, 126, 127, 130 Azurin, 373-375 Bacteria, 424, 427 Bacterial photosynthetic system, 385-386 Bacteriophage, 180-182 Bacteriophosphyrin, 387 Bacteriorhodopsin, 283-293 Barbiturates, 425 Barium (Ba), 159, 376 Base stacking, 142, 150, 155 Base vibrations, 135-138 Bathorhodopsin (prelumirhodopsin), 272, 274-277, 280 Baygon,426 Bonding vibrations, 20, 26, 27, 30, 32, 204, 274-276 Benzamphetamine, 425 Benzene, 23, 27, 33, 107, 202 S-Benzyl-Cys- Pro- Leu-Gly NH" 77 Beta (f3)-sheet, 70, 72-76, 78-83, 85, 86, 98, 99, 107, 176, 179, 180, 182,212,214, 222, 403. See also Antiparallel-{3-sheet Beta (f3)-turn (3 10 helix), 72, 76-79, 85, 176 Bilayer, 188, 189,202,208,211,213,214,217 Binuclear-cluster-type Fe-S linkage, 306 Biological membranes, 187-225 Bioluminescent bacterium, 57 Bleomycin, 164

Blood, 108, 259, 422 Blood coagulation, 108 Bonding, 327 Bound water, 405 Breathing vibration. 32, 33, 90, 100, 101 cyclic compound, 32 Breathing vibration, proteins, 100. 101 Bromide, 213, 332 B-type cytochrome, 318 Buried tyrosine, 87-89 Cadmium (Cd), 126, 159 Calcium (Ca), 158, 159, 161,219,223,376,377, 399,404,405 Calcium carbonate stones, 416 Calcium oxalate, 416 Calcium phosphate stones, 416 Calculi, 416 Carbohydrate, 129,234-253 Carbohydrate-lipid interaction, 251, 252 Carbon dioxide, 8, 9, 21, 23-26 Carbonic anhydrase, 85, 107, 125-127 Carbon monoxide ligand, 334, 335 Carbonmonoxyhemoglobin (HbCo), 57, 335, 350 Carbon tetrachloride (CCI,). 39, 40 Carbonyl (C=O) stretching vibration, 36, 38, 57,68,70,79,96,97,136,137,151-153, 159,160,175,17"5,206,208,215,246, 247,277,324,326,356,384 Carbonyl stretching vibration, carbohydrate, 246-248 Carbonyl group: carbohydrates, 245, 246, 248 stretching vibration, nucleic acids, 136, 139 vibration, 36, 68,137,245,246,311,312, 198, 199 Carboxyhemoglobin, 334 Carboxypeptidase A, 121, 122 Cardiolipin, 210 {3-Carotene, 219, 223, 256-260, 387 Carotenoiq, 223, 224, 256-262, 381, 386, 387, 419,423 in carrot-root cell, 419 in membranes, 223, 224 in photosynthesis, 386, 387 Carrot, 258, 419 CARS (coherent anti-Stokes Raman spectroscopy), 41, 54-58, 257, 265, 334 flavins, 265 Cataracts, 396-398 Catecholamines, 424 C-C stretching vibration lipids, 192-196, 201-204,207,210,213,216, 219, 221,22~ CDEC (2-chloroallydithiocarbamate), 426 Cerebronic acid, 205 Cerebroside, 205, 206 Ceruloplasmin, 370, 372-375 Cesium (Cs), 376

Index C-H vibration, 27, 31, 32, 36, 234, 244, 245, 248, 249, 274, 285, carbohydrates, 244, 245, 248, 249 lipids, 194-199,201,203-207,210,213,214, 218,219,221,224,225 methane, 34 methylene group, 27, 31 methyl group, 31, 32, 274-276, 285, 286 protein, 65, 81, 96 Channel protein, 189 Chemical modification, proteins, 106, 107 Chitin, 246, 251 Chlordane, 426 Chloride, 213, 332, 334 Chlorinated-hydrocarbon pesticides, 426 Chloroperoxidase, 332 [I-O-Chlorophenyl-)-I-(P-chlorophenyl)2,2,2-trichloroethane],426 Chlorophyll, 382-385, 423 Chlorophyll a, 382-384 Chlorophyll a-protein complex, 385 Chlorophyll b, 382-384 Cholesterol, 208, 215, 217, 218, 221 Chondroitinsulfatc, 240, 241, 247, 251 Chromatin, 135, 182 Chromium (Cr), 158,302, 330 Chromosome, 182-185 Chymotrypsin, 70, 86, 100, 10 I, 103, 120, 125 Chymotrypsinogen, 71, 75, 76 CIPC (chloropham), 426 Circular dichroism (CD), 65,66,75,81,84,86, 300 Cis amide, 79, 80 Cis isomer, 199,200 Classical mechanics of Raman scattering, 12-14 Clinical analysis, 424, 425 Clinical application, 422 Clinical diagnosis, 422 CMP, 142, 166 Cobalt (Co), 158, 159, 161,302,309,321,323, 327, 348, 354, 376, 377, 389, 427 Cobalt corrinoid, 389 Coherent light. 46, 47 Collagen, 398, 399 Combination band, 39, 67 Compton effect, 434 Computer, 50-53 Computer subtraction, 290 Conformation: carbohydrates, 249-251 nucleic acid, 145-153 protein, 73-78 Contractile state of muscle, 405 Co(II)-carbonic anhydrase, 376 Co(II)-carboxypeptidase, 376 Co(II)- imidaZOle, 376 Co(II)-mesoporphyrin IX, 348 Co(II)-octaethylporphyrins, 321

439

Co(JI)-porphyrin, 354 Copper, 158, 159,161,162,213,209,302, 321-323" 325, 326, 348, 369-376, 418 in biological systems, 369-376 Copper (Cu)-N bond vibration, 371-375 Copper (Cu)-S bond vibration, 372-375 Copper-D-penicillamine, 374 Copper protein, 372 Core expansion theory, 353, 354 Cornea, 398, 399 Corrinoid, 389 CoO stretching vibration, 334, 335 CPG, 150 Cryoglobulin, 130 CoS stretching vibration, 38, 93-96, 104, 322, 425 cytochrome c, 322 C-type cytochrome, 318 Cubane-type Fe-S linkage, 307 Cu-mesotetraphenylporphyrin, 348 Cu-octamethylporphyrin, 348 Cu-peptide complex, 375, 376 CuS, 373, 418 Cu(II)-mesoporphyrin IX, 348 Cu(II)-octaethylporphyrin, 321 Cu(II)-sulfur complexes, 373 Cu(II)-transferrin, 375 Cu(JI)-uroporphyrin I, 322 Cyanide (CN), 326, 334, 388 Cyanocobalamin, 388 Cyclic compounds, 32, 33,240, 249, 250, 252, 376 Cyclic oligoamylose, 252 Cycloheptaamylose, 252 Cyclohexaamylose, 240, 249, 250 Cyclo(L-Pro-Gly)" 376 Cysteinato ligand, 311 Cysteine, 96, 97, 372 Cystine, 94-96, 309 Cytidine, 143, 159, 160 Cytochrome a, 318, 324, 331, 347 Cytochrome a oxidase, 356 Cytochrome aJ, 318, 324, 326, 342, 343, 347, 356 Cytochrome aJ oxidase, 356 Cytochrome b, 317, 344, 355 Cytochrome b" 319, 344, 346 Cytochrome b ,6l , 356 Cytochrome b"2, 333 Cytochrome b"" 356, 357 Cytochrome c, 53, 54, 57, 59, 317, 319, 322, 323,331,333,337,340,342-345,348, 352, 355, 357 Cytochrome c', 332, 333, 343 Cytochrome C1, 344, 355, 356 Cytochrome CJ, 333, 344 Cytochrome em, 333 Cytochrome Cm, 323 Cytochrome Cm, 323

440

Index

Cytochrome cd, 59 Cytochrome c oxidase, 210, 345, 346, 356 Cytochrome c peroxidase, 331, 344, 346 Cytochrome!,333 Cytocrhome oxidase, 318, 344, 345, 347, 356 Cytochrome P-450, 330, 331, 340, 342, 344 Cytosine, 142, 147, 148, 154, 155, 175 Dark-adapted bacteriorhodopsin, 58, 283, 292" 293 DDT,426 O,P' DDT, 426 Degenerate, 24, 205 Degenerate bending, 24 Degree of antisymmetry, 35 Degree of freedom, 12, 25, 27 Delhaye molecular microprobe, 411 Denaturation, proteins, 103-106 Deoxyhemoglobin, 334, 339 Depolarization, 346, 349 Depolarization ratio, definition, 33-36 Dermatan sulfate. 247 Deuterium exchange, 38, 70, 71, 79, 80, 85, 97,101,107,135,136,140,141,152, 197,198,202,236-240,246,252,277, 278, 289 Deuteroheme, 323 Dextransulfate, 247 Diamine oxidase, 377 Diatomic molecule, 21, 22 2,4- Dichl oro benzylt ri butyl Ph os p honi u m chloride, 426 cis-Dichlorodiamine platinum, /60 Dichlorvos, 426 Dicofol, 426 Dieldrin, 426 0- 0- Diethy1- 0-(2,4-d ic hloro phe nyl)phosphorothioate, 426 Dila uroylphosphatidylethanola mine (D LPE), 203-205 4- Di met hyla mi no-3-n it ro( cr-benza mid 0 cinnamate), 118, 119 Dimyristoylphosphatidylcholine (D M PC), 198,202,203,210,212,213,218,224 Dinactin, 69, 215 Dioxygenase, 303, 305, 374 Dipalmitoylethanolamine, 202 Dipalmitoylphosphatidic acid, 203 DipalmitoylphosphatidyJcholine (DPPC), 194, 198,201,203,205,206,208,210, 211,212,218,220 Di pal mi toylph os p ha tid ylet ha nola mi ne (DPPE),219 Diphenhydramine, 425 Dipiocolinate, 427 Dipole moment, 14, 15, 20, 22, 23-26, 28-30 Distamycin A, 164, /65 Disteraoylphosphatidylcholine (DS PC), 202 Disulfide (S-S) stretching vibration, 38, 66, 83, 91-94,96,104-106,176,179, 180,310, 373,397,398,418

DNA, 57,145-149,155,157,160,163-166, 180-185,412 Dopamine-{3-hydroxylase, 370 Dopier effect, 434 Diamagnetism, 330 Drugs, 128, 129, 163-165, 252, 425 interaction with nucleic acids, 163-165 Dual-beam method, 279 Dye laser, 48 Egg white protein, 93 Elbow-bending, 102 Electric dipole transition moments, 17 Electric field, 4, 12 Electric vector, 3, 4 Electromagnetic molecular electronic resonance, 103 Electromagnetic wave, 3-5 Electron cloud, 8, 9, 21-30 Electronic time gate, 41 Emulsion, 188, 189 Enamel,418 Endoplasmic reticulum, 204, 205 Endosulfan, 419, 426 Endrin, 426 Enhl'drina schis/osa toxin, 71 Environmental applications, 419, 420, 422, 425-427 Enzyme-drug interactio"l' 128, 129 Enzyme-inhibitor complexes, 125-128, 305 Enzyme, 117-129 Ephedrine, 425 EPIC (ethyl-N-dipropyl-3chlorophenylcarbamate),426 Epinephrine, 424 EPR, 303, 331 Equatorial C-H vibration, 235, 239, 240, 241 Erythrocyte, 36, 210, 212, 219, 220, 222, 223 Erythrocyte ghost, 36, 220, 222, 223 ESR, 207, 209, 222 Ester, 36, 68,137, 190 Ethidium ~romide, 165 Ethion,426 Ethylene, 23, 27 Etiporphyrins, 325, 326, 337, 341 Excitation profile, 47,262, 322 carotenoids, 262 Excitation wavelength (frequency), 18,40,41 Exposed tyrosine, 87-89 Eye, 270-272, 281, 395, 398 Fatty acids, 188, 190-/92, 198, 199,207,208 Fe-N bond, 334, 337-340, 343, 352 Fe-O stretching, 299, 30 I, 304, 312, 341, 335-339 Ferbam, 426 Fermi resonance, 87, 196 Ferredoxin, 306-308, 374 Fe-S, 306-310 Fibrin, 108 Fibrinogen, 108,209

Index Fifth ligand, 333, 342, 352, 353 Fish guanophore, 418 Flavin, 57, 262-266 Flavinadeninedinucleotide (F A D), 57, 262-265 Flavinmononucleotide (FMN), 57, 262-265 Flavocytochrome c, 266 F1avocytochrome Cm, 265, 266 Flavodoxin, 264 Flavoenzyme, 262-266 Florescence, 40, 57. 65, 103,203, 303 Fluorescence spectroscopy, 65 Fluoride (F-), 334, 399 Food additives, 426-427 Foreign bodies of silicone rubber within multinucleated giant cells, 415 Formyl group, 324-326 Free energy of cooperation, 350 Frequency, definition, 4 Frequency difference, 10 Frequency doubler, 18 Fundamental vibrations, 20, 24, 25, 27, 67, 196,200 Furadan.426 {3-(2-Furyl)acryloylphosphate, 124 Galactosamine, 245 Galactose, 206, 212 Gamma (I')-turn, 72, 76, 78 Gauche conformation, 91, 92, 93, 95,192-196, 205,206,208,209,211-213,219,220 Gauche form, methionine, 95 Gauche-gauche-gauche conformation, 91-93 Gauche-gauche-trans conformation, 91-93 Gel, 75,152,153,192,193,197,202,205,208, 211,215,218 Gcl phase, 191-193,201,202,205,207,215 Geometry of the heme ring, 352-354 Glucagon, 83, 210 Glucosamine, 235-239, 245 Glucose, 235-240 Glucose oxidase, 264 Glucose sulfate, 247 Glucuronic acid, 235-239, 246 Glutamic acid, 79, 300 Glutathione peroxidase, 377 Glyceraldehyde-3-phosphate dehydrogenase, 124 Glycerol, 188, 202, 203 Glycophorin,212 Glycoprotein, 108,212 Glycosidic linkage, 235, 241, 249 Glycosphingolipid, 212 Glycylglycine complexes with Cu(II), 375 Gly-Gly,82 Gly-Tyr,87 GMP, 135, 143, 153, 156, 159, 160, 166 GpA,136 OpC, 150 OpG,153 Oramicidin A, 214, 215

441

Oramidicin D, 216 Gramidicin S, 77, 216 Griseofulvin, 425 Group frequency, 36-38 Guanine(G), 142, 148, 151, 153-155, 159, 160, 175,415,418 Guthion, 426 Hapten, 129, 130 Hard metal, 158 Harmonic oscillation, 19 Heat treatment, nucleic acids, 141 Hematoporphyrin, 321 Heme, 266, 316-357 structure of, 324 Heme 0, 344, 345, 347 Heme 03,345 Heme IX, 344 Hemerythrin, 299-301, 374 Hemeundecapeptide, 317 Hemocyanin, 370, 371, 374 oxygen in, 370, 371 Hemoglobin, 57, 330, 334-342, 344, 346, 349-352, 354 Heparin, 247, 25 I Heparin sulfate, 247 Heptachlor, 426 Hexacoordinated complex, 353 Hexacoordination, 342 Hexopyranoside, 241 Hinge-bending, 102 Histidine, 91,107,209,300,311,333 Histone, 70, 182-185 Hooke's law, 19 Horseradish peroxidase, 344, 346 Hyaluronic acid, 240,241,242,246 Hydralation, 84, 101 Hydrocarbon backbone, 201-203 Hydrochloric acid (HCI), 21,434 Hydrogen bond, 38, 79, 87,153,212,214,219, 242, 252, 273 nucleic acids, 150, 151, 153, 154 protein, 79, 81, 87, 106 tyrosine hydroxyl group, 87 Hydroxo ligand, 311 1- Hydro xy(2,4-d ini trop henylazo)-2,5naphthalenedisulfonic acid, 130 Hydroxy, (-OH) group, 36, 96 Hydroxylapatite, 399, 400 IgA,130 IgO, 86,101,129,130 IgM,130 Imidazole, 91 Immunoglobulins, 102, 129, 130 IMP, 142 Inaugural lecture, Raman, 431 Indole-ring vibration, 89, 90 Induced-dipole moment, 8, 12, 14, 15,21 Inosine, 142 Inositol hexaohosohate, 351

442

Index

In-phase stretching vibration, 33 In-plane vibration, CO" 24-26 methyl group, 31 Insulin, 73, 83, 104, 108,210 Intensity of Raman lines, 10-12 Intermolecular vibrations, 101, 102 Internal vibrations, 100, 101 Inverse polarization, 347 Iodide 252, 332 Iodine, 213, 252 Iodine-starch complex, 252 lon-lipid interaction, 213 IPC (isopropyl-N-phenylcarbamate, prophamJ, 426 I R (infrared), 4, 5, 15, 16,21-28,33,36,42,43, 45,50,58,71,78,81,82,97,99,159, 185, 190, 222, 234, 242, 255, 334, 426 Iron (Fe), 158,298-312,327-332,338,339, 341-343, 346, 352, 377 Iron (Fe) ligand band, 337-343, 352 Iron-sulfur proteins, 306-310 Isoalloxazine, 263 Isoleucine, 89 Isomers, 326 Isorhodopsin, 274-277 Isotopes, 38-40 Isotopic substitution, 38, 40 Isozymes, 128, 129

(n

Jet-stream technique, 280 Kerasin, 205 Keratin, 79 Keratin sulfate, 247 Keto carbonyl group, 386 Ketone, 36, 137 Kidney stones, 415 Laccase, 373-375 Lactoferrin, 302, 304 ,a-Lactoglobulin, 74 Lactose, 240 Lamellar liquid, 207 Lapemis hardwickii toxin, 70, 71 Laser, 9, 18, 40, 44-49, 97, 334 Laser tubes, 18,47-49,51 Lateral interaction, 207 Lateral packing, 197, 199,208 Laricauda semifasciara neurotoxin, 103 Lattice vibrations, 102, 191,252 Lauric acid, 191, 192 Lead (Pb), 159 Leghemoglobin, 336, 343, 354 Lens, 396, 398 Leucine, 89 Ligand, 332, 371, 372 Ligand-sensitive Raman bands, 333 Light meromyosin, 403 Lignoceric acid, 205

Lindant, 426 Linkage in bacteriorhodopsin, 288-293 Linkage in rhodopsin, 277-279 Lipid, 187-225 Lipid-antibiotic interaction, 213-218 Lipid-carbohydrate interaction, 251, 252 Lipid-ion interaction, 213 Lipid-lipid interaction, 207, 208 Lipid-protein interaction, 209-213, 221 Liposomes, 188, 189,211-214 Lippert's equation, 85 Liquid crystalline, 192, 193, 197,201,202,205, 207, 208,211,215,218 Lobster shell, 261 Longitudinal acoustic vibrations, 101, 191 Low-frequency vibration, 99-102,191,192, 194, 235, 340, 341 lipids, 190- J 92, 194, 320 proteins, 99-102 Lumazine protein, 57 Luciferin, 419 Lumazine protein, 264, 265 Luminavin, 266 Lumirhodopsin,272 Lutein, 260 Lycopene, 257, 258 Lymph node, 414-416 Lymphocytes, 225, 226 Lyophilization, 83, 84 Lysine, 130, 209, 288, 333 Lysozyme, 52, 78, 81, 83, 86, 93, 101, 103, 104,212 Magnesium (Mg), 144, 156, 158, 159, 161-163, 213, 224, 341, 376, 377, 382, 384, 399 Magnetic field, 4 Magnetic vector, 3,4 Malathion, 426 Maltose, 240, 250 Maltotriose, 250 Mammary carcinoma, 422 Mammary tissus:s, 423 Maneb,426 Manganese (Mn), 158, 159,302,321,377 Maser, 45 Maximum number of vibrations, 21, 27 Melittin, 210, 211 Melting temperature (T m ), 154,191,192,197, 201-203, 205, 206 Melting, tRNA, 154 Membrane, 187-225 Membrane potential, 260, 262 Membrane proteins, 222-224 Mercury (Hg), 158-161,416 Mercury lamp, 45 Mesoheme, 323 Mesotetra-(a,a,a,a-pivaloylamidophenyl) porphyrin, 337, 342 Mesotetraoxyhemoglobin, 337

Index

Meso-tet ra phenylporphinato -bis(tetrahydrofurna)-Fe(II),354 Messenger RNA (mRNA), 155 Metabolic time process, 427 Metal ion, interaction with nucleic acids, 158-163 Metarhodopsin, 272, 281 Methamphetamine, 425 Methemerythrin, 300 Methemoglobin, 343, 351 Methionine, 66, 94-96, 333, 373 Methotrexate, 128 Methoxychlor, 426 Methylene vibration, 86, 204, 210 Methyl group (CH,) vibrations, 31,32, 101, 199,204, 205, 214, 222, 274, 276, 382 Methylene group, vibrations, 27, 31, 199 7- Methylguanosine, 156, 157 Methylelaidate, 200 Methyllaurate, 200 Methyllinoelaidate, 200 Methyllinoleate, 200 Methyllinolenate, 200 Methyloleate, 200 Methylparathion, 426 Meting, nucleic acid, 147-150, 154 Metmyoglobin, 343 Mevinphos, 426 Micelle, 188, 189 Microbial cells, 423, 424 Microprobe, 413 Microwave, 45, 424 Midtransition temperature (Tm), 191, 192 Mineralization in kidneys, 416 Mitochondria, 209, 354-356 Mixed vibration, 70 Mojave toxin, 83 MOLE (molecular optical laser examiner), 411,414,418,420 clinical and histological applications, 414-419 Molybdenum (Mo), 312, 377 Monactin,69 Monochromator, 48, 50 Monolayer, 188, 189 Monooxygenase, 303 Monostearin, 251, 252 Multichannel analyzer, 53, 398, 412 Multilayer, 188, 189,207 Multiple wavelength detectors, 53 Mu (Il)-oxobridged ligand, 311 MUSCle, 80, 395, 401-405 whole, 405 Mu (Il)-sulfide bridge, 300 Mutual exclusion, principle of, 23 Myelin sheath, 212 Myoglobin, 321, 330, 336, 338-341, 344, 354 Myoglobin-carbon monoxide complex (MbCO), 334, 335

443

Myosin, 401, 402, 405 Myosin subfragments, 403, 404 Myotoxin a, 70 NAD,137 NADPH, 128, 167 Neoprontosil, 126 Nerves, 224, 225 Netropsin, 164 Neurotoxins, 103-105 New yellow enzyme, 265 N-H stretching vibration, 38, 67, 68, 70, 245 N-H vibration, carbohydrates, 245 Nickel (Ni), 159, 319-321, 348 Nicotine, 426 Ni-mesotetraphenylporphyrin, 348 Ni-octaethylporphyrin, 320 Ni-octamethylporphyrin, 348 Nitrate analysis, 427 Nitrobenzene group, 118 Nitrogenase, 312, 374 Nitro group vibration, 97 Nitrogen molecular (N2), 21 Nitrosylhemoglobin (HbNO), 351 Ni(Il)-octaethylporphyrin, 321 Ni(1I)-mesoporphyrin IX, 348 NMR, 202, 222, 352 Nobel lecture, 434 Nobel Prize, 434 Nonactin, 215, 216 Noncoherent light, 48 Nonheme iron compounds, 298-312 Non-histone proteins, 183, 184 Non-totally symmetrical vibrations, 35, 36 Noradrenaline, 424 Norepinephrine, 424 Normal coordinate, 20 Nucleic acid, 59, 103, 134-167 Nucleoprotein, 174-185 Nucleosome, 182-185 Nystatin, 218 Occular lenses, 395 Octaethylporphyrin, 319, 330, 338, 339 Octahedral, 342 O-H vibration, 20, 242-244, 248 carbohydrates, 242-244, 248 definition, 20 Old yellow enzyme, 265 Omega-helix, 78 O,P' DDT, 426 Opsin, 272, 282, 283 Optical maser, 45 Optical microscope using Raman effect, 411 Order parameter, 207 Out-of-plane vibration: CO 2 , 24, 27 methyl group, 31 Ovalbumin, 76, 107

444

Index

Overtone, 67, 196 Ovorubin, 262 Ovotransferrin, 302, 304 Oxalate stones, 416 Oxidation state, 343-346 Oxidation-state marker band, 344 Oxidative phosphorylation uncouplers, 222 Oxygenase, 303-306 Oxygenation, 335-337 Oxygen (0,), bound to hemerythrin, 299, 300 Oxygen (0-0) stretching vibration, 299, 300, 321, 335-33~ 339, 370-372 Oxyhemocyanin, 300 Oxyhemoglobin (HbO,), 300, 335, 336, 339, 351 Oxymyoglobin, 321 Oxytocin, 70, 71, 77 Oxytocin agonist, 83 Oxytocin antagonist, 83 Oxytyrosinase, 372 Paleontology, 420 Papain, 117-120 Paradium (Pd), 348 Paramagnetism, 327 Parathion, 426 Pd-mesotetraphenylporphyrin, 348 Pd-octamethylporphyrin, 348 Pelamis platurus neurotoxin, 105 [I -Penicillamine,2-leucine]-oxytocin, 92 [I-Penicillamine]-oxytocin, 78, 92 Pentacoordinated complex, 352, 353 Pentacoordination,342 Peptide backbone, 66, 70, 103, 104,397 Peptide bond vibration, 66-72, 75 Pepulate, 426 Perchlorate (ClO~), 213 Permanent electric dipole moment, 21 Peroxidase, 123, 322, 331, 338, 339, 343 Peroxide, 300 Peroxo ligand, 311 Perthane, 426 Pesticides, 419, 426 Phage, 180, 181,211 Phage fd, 181,211 Phage MS2, 180 Phage, P22, 180 Phage PfI, 181 Phage RI?, 180 Phendimetrazine, 425 Phenolate, 311 Phentermine, 425 Phenylalanine, 90, 350 Phenylamide, 426 2-Phenylethane-boronic acid, 125 Phosphate, 128, 139 Phosphatidylcholine (PC), 204, 205, 208, 215 Phosphatidylethanolamine (PE), 197, 204, 205

Phosphodiester-bond stretching vibrations, 141-143,145,147,151,154,155, 157-159,161,176,178 Phosphoionic bond vibrations, 144, 145, 155, 158,162,178,195,196,212,213,219, 220 Phospholipid, 187-225 Phosphorus, 399 Phosphorus-containing pesticides, 426 Photochemical cycle, 272, 284 Photomultiplier, 41,48, 50 Photoreduction, 345, 351 Photosynthetic pigments, 382-387 Phrenosine, 205, 206 pH treatment, nucleic acids, 141 Phycobilins, 381 Phycocyanin, 26 J, 387 Pi (7T)-helix, 72 Planck's constant, 17, 19 Plant photosynthetic system, 384-385 Plant viruses, 175-180 Plastocyanin, 370, 373, 374 Platelet, 260 Platinum (Pt), 159, 160,321 Polarizability, 8, 12, 13, 14, 21-30, 34 isotropic, 34 Polarizability derivative

(~Q)' 21-26, 28-30

Polarizability ellipsoid, 21-3') Polarizability tensor, 17 Polarization, 346-349 Polarizer, 33-35 Poly(A), 135, 138-140, 142, 143, 150, 152, 15~ 158, 167 Poly(A,G) • poly(U), lSI Poly(A) • poly(C), 145 Poly(A). poly(U), 147, 150 Poly(A-U). poly(A-U), 150 Poly(,B-benzyl-L-Asp), 69, 78 Poly(C). 138-140, 142,143,151,152,158 Poly d (A-T), 157 Poly(DL-Ala), III Poly(G), 138, 139, 144 Poly(G) • poly(C), 144 Poly(Y-benzyl-L-Glu), 69, 73, 82 Poly(Gly), 69, 73, 74, 99 Poly(I), 138, 139, 142, 151, 152 Polyiodide, 252 Poly(L-Ala), 69, 73-75, 80, 81, 100 Poly( L-Ala-Gly), 74, 75 PolY(L-Arg), 158 Poly(LGlu), 69, 73, 80, 81, 97, 98 PolY(L-His),69 POlY(L-Leu), 69, 80 PolY(L-Lys), 69, 73, 74, 80, 86, 97, 98, 158, 211 PolY(L-Met), 80 POlY(L-Pro),68 Poly(L-Tyr, L-Lys), 375

Index Poly(L-Val), 74, 82, 83, 99 Polypeptides, interaction with nucleic acids, 157, 158 Polyphenoloxidase, 370 Poly(U), 136, 138-140, 142, 144, 152, 167 Population inversion, 45-47 Porphin, 348, 349 Porphyrins, 316 Potassium (K), 216, 376 Praseodymium (Pr), 159 Pre melting, 202 Preresonance Raman spectroscopy, 16,97,98, 165-167 Principle of mutual exclusion, 23 Probe laser, 55 Proflavin, 266 Proinsulin, 108 Pro-Leu-GlyNH 2 ,77-80 Protein, 65-108 effect on water, 84 Protein environment, hemeproteins, 352 Protein-lipid interaction, 209-213, 221 Protocatechuate, 374 Protocatechuate 3,4-dioxygenase, 128, 303-305 Protocatechuate 3,4-dioxygenase tyrosine, 377 Protoheme, 323 Protonated Schiff base, 277-281, 288-293 Pseudo-Raman, 103 Pulsed laser, 41, 53 Pumping, 45, 46 Pump laser, 55 Purine compounds, 415 Purine-ring vibrations, 136 Putidaredoxin, 307 Pyrazine, 23, 27 Pyrimidine dimer, 147 Pyrimidine-portion vibrations, 136, 137 Pyrocatechase, 304-306 Pyroglutamyl residue, 79, 80 Pyrole, 23, 27 Pyruvate carboxylase, 377 Qualitative estimation, phospholipid conformation, 206, 207 Quantitative estimation, protein structures, 84-86 Quaternary structure, 332, 349, 351, 352 Ramachandran angles, 66, 70 Raman, C. V., 430 first paper, 434 last pa per, 434 Raman band assignment, 382-384 Raman circular intensity differential (Raman ClD), 58, 59 Raman difference spectroscopy (ROS), 53-55 Raman dispersion, 47, 48, 318

445

Raman hyperchromicity (Raman hyperchromism), 15, 16, 152, 175 Raman hypochromism, 15, 16 Raman microprobe, 411, 413 Raman microscope, 41 I Raman optical activity (ROA), 58, 59 Raman-scattering tensor elements, 17 Raman spectra: background, 103 bacteriorhodopsin, 58, 291 benzene, 16 blood plasma, 259 ca rbon tetrachloride, 39 carrot (live root and canned juice), tomato fruit, {3-caroteine and Iycopene, 258 copper-etioporphyrin isomers, 325 cyanomethyl-2-aceta mide-2-deoxy-l-thio {3-D-glucopyranoside, 248 cytochrome c (ROS spectrum), 55 cytochrome c (resonance Raman), 345, 348 dipalmitoylphosphatidylcholine (0 M PC), 194 ON A (type A and type B), 146 erythrocyte ghost, 220, 221 fatty acid (low frequency region), 192 glucose, 243 hydroxylapatite, 400 lens, 397 lysozyme, 52, 104 mammary tissue (normal and cancerous), 423 a-methyl-D-glucoside and {3-anomer, 244 mitochondria (whole), 355 mole spectra: foreign body in lymph node, 416 crystals in tissues, 418 myosine and whole muscle, 405 oxyhemoglobin, 336, 341 papain-substrate complex for resonance Raman, 119 all-trans-retinal-n-butyla mine hydrochloride, 278 rhodopsin, 279 sea snake neurotoxin, 105 of solid and aqueous samples, proteins, 83, 84 sulfhydryl group of sea snake neurotoxin, 96 sulfhydryl group of TMV proteins, 179 teeth,400 tobacco mosaic virus, 178 its coat protein, 178 its RNA, 179 tyrosine bands, 87 {3-uridine-5'-phosphoric acid, 166 Raman spectra background, 103 Raman spectrometer, 48, 50-53 Random coil, 73, 74, 78-81, 85, 103, 179, 180 Ratio of anti-Stokes to Stokes lines, 10-12 Rayleigh scattering, 6, 7, 9, 13, 191

446

Index

Reaction center, 260, 385, 386 Redox potential, 356 Reduced mass, 38 Relative-intensity parameter, 211, 215 Renal lithiasis, 415 Resonance Raman spectroscopy: bacterial cells, 422, 423 bacterial rhodopsin, 283-293 carotenoids, 256-262, 419 CARS, 54-58 chlorophylls, 381-387 copper and other metal compounds, 369-377 definition, 16-19 drug analysis, 424, 425 enzymes, 117-128 flavins, 262-266 food additives, 425-426 hapten, 129, 130 hemes and porphyrins, 316-357 laser for, 47 membranes, 219 nonheme iron compounds, 298-312 nucleic acids, 165-167 rhodopsin, 270-282 sulfhydryl group, 97 theory, 16-19 visual pigments, 270-282 vitamin B 12 , 387-389 Retina, 270, 271 Retinal, 272, 275-277 II-cis-Retinal, 272, 273, 275, 277 13-cis-Retinal, 274-277 all-trans-Retinal,272-276 R form, heme proteins, 343, 350 Rhodopsin, 270-283 Ribonuclease, 75, 76, 81, 83, 86, 87, 90, 93,157 Ribose, 138, 139 Ribose-phosphate vibrations, 139 Ribose-ring vibrations, 136 Ribosome, 153, 154, 155, 156 RNA, 144, 145,147,153,155,156,165,166, 175-180 Rocking vibration, 31, 204, 275, 285, 286 Rotational quantum level, 5 R state, heme proteins, 335, 349, 351, 354 Rubidium (Rb), 376 Rubredoxin, 308, 309, 374 Ruthenium (Ru), 376 Ruthenium red, 376, 377 Sarcoplasmic reticulum membranes, 223, 224 Scaling constant, 85 Scattering: definition, 6-14 elastic, 6, 7 inelastic, 6, 7 Schiff base, 277-279, 288-293 Scissoring vibration, 204, 205 Sea snake neurotoxin, 85, 87, 89, 90, 96, 97, 103-106 Secondary IinkaJ!e, bacteriorhodopsin, 288

Selenium (Se), 374, 377 Selenocystine, 374 Serum transferrin, 304 Side chain, 86-97, 104-106,322-325 proteins, 86-97 Signal averaging, 41, 53 Signal-to-noise ratio, 41, 53 Silver (Ag), 158, 159, 264 Simian virus 40 (SV40), 225 Sixth ligand, 333, 342, 352, 353 Skew-skew conformation, 20 I Smoothing, 52 Snake neurotoxin, 83, 85, 87, 89,93,96,97, 103-106 Sodium (Na), 158 Soft metal, 158 Sonication, 203 Soret band, 317, 346 Spheroidene, 260 Sphingomyelin, 203-205 Sphingosine, 206 Spider, 417 Spider cuticle, 415 Spin, 309, 327, 330, 331, 334, 346, 357 Spin labelling, 207, 218 Spin-sensitive Raman bands, 326, 331 Spin state, 326-332 Square pyramidal, 342 Starch, 249-252 Starch-iodine complex, 252 Steady-state concentration, 285 Stearic acid, 192, 205 Stellacyanin, 372-374 Stimulated-emission process, 45, 46 Stokes effect (Stokes Raman scattering), 6-14, 56 Streptococcus faecalis membrane, 224 Streptomyces subtilisin inhibitor, 93 Subunit interactions, 101, 102 Succinate-cytochrome c reductase, 318 Sulfates, 213, 245, 247 Sulfhydryl groufJ (-SH), 38, 66, 96, 97, 106, 176, 177, 179,234,263,397,398 Sulfonamide, 425 Sulfonamide inhibitor, 125, 126 4-Sulfonamido-4'-aminoazobenzene, 126 4-Sulfonamido-4'-dimethylaminoazobenzene, 126 Sulfur-containing pesticides, 426 Sulfur dioxide (SO,), 27-30 Superoxide, 300 Superoxide dis mutase, 377 Superoxo ligand, 311 Surface-enhanced Raman spectroscopy (SERS),59 Symmetrical ring vibration, 241 Symmetrical stretching vibration, 21-24, 27, 28,31,32,39,91, 197, 199,203-205, 245, 247,299,312, 320 Symmetry: center of, 23

Index Stokes and anti-Stokes lines, 9, 10 of vibrations, hemes, 319-321 Synthetic polypeptide, 69, 73, 82, 83 Tautomer, histidine. 91 Tautomerism, 135 TDE,426 Teeth, 395, 399, 400 Temperature effect: cryoglobulin, 130 heme, 357 lipids, 192, 197 nucleic acids, 147-149 on Raman intensity, 10-12 Terminal CH" 197, 203 Terradifon, 426 Tetraglycine,( GLY)" 82 Tetrahedron-type Fe-S linkage, 307 Tetraphenylporphyrin, 346 Theory: Raman microprobe, 412-414 Raman spectroscopy, 3-43 Thermotropic transition (T m), 191, 192 Time-resolved resonance Raman spectrocopy, 257 Thiocyanate (CNS-), 213 Thiohexopyranoside, 241 Thiomolybdate, 377 Thiram, 426 Thymidylate synthetase, 123, 124 Thymine, 136, 148, 160, 175 Thymocytes, 225 Thyroid releasing factor, 79, 80 Tobacco mosaic virus (TMV), 97,175-177 Tolbutamide, 252 Toluene, 15, 16 Tomato, 258 Torsional angles (Ramachandran angles), 66, 70 Torsional vibrations, 101 Totally symmetrical vibrations, 35. 36 Total number of vibrations, 20 Trans amide, 79 Trans conformation, 192-195, 199-20 I, 205, 206, 208, 209 Trans~rrin, 302, 303, 375, 377 Transfer RNA (tRNA), 150, 153-156, 167 Trans-gauche-gauche conformation, 92, 93 Trans-gauche·trans conformation, 91-93, 104 Trans isomer, 199, 200 Transition enthalpy, 206 Transition temperature (Tm ), 191, 192, 197, 211,215 Transmembrane potential, 224 Triatomic molecules: linear, 21 nonlinear, 25, 27 Tributyl phosphorotrithioite, 426 Trichinopoly, 430 Triclinic paraffin, 191 Triclinic polyethylene, 191

447

Trielaidin, 200 Trilinoelaidin, 200 Trilinolein, 200 Trilinolenin, 200 Triolein, 200 Tripalmitin, 204 Tropomyosin. 80, 401, 404 Traponin, 401, 404 Trypanocidal drug, 165 Trypsin, 127 Trypsin inhibitor, 86 Tryptophan. 66, 89, 90,97, 106, 107 T state, heme compounds, 335, 349, 350, 351, 354 Tumor, 423 Tunable laser, 18,48 Turnip yellow mosaic virus, 177, 179, 180 Twisting vibration, 31, 200, 204 Type 1 copper, 369, 370 Type 2 copper, 369, 370, 375 Type 3 copper, 369, 370, 375 Tyrosinase, 370 Tyrosine, 66, 83, 87-89, 90, 107, 122, 177, 283, 300, 304-306, 383 UMP, 160 Unsaturated fatly acids, 199·201 Unstacking of bases, 154 UpA,I50 Uracil (U), 142, 151, 154, 155, 175 Uric acid, 415 Uric stones, 416 Uridine, 143, 159 I3-Uaridine-5'-phosphoric acid, 165, 166 Uteroferrin, 303 UTP, 166 Valine, 89, 217 Valinomycin, 69, 198, 217 Vibration, origins. heme, 319-322 Vibrational assignment: amide I, 74, 76, 77, 81, 98 amide III, 73, 74, 76, 77, 81, 86, 98 bacteriorhodopsin, 285-287 carbohydrates, 236-240, 246. 247 chlorophylls, 383 CuN and CuS, 373 FeS, 309, 310 Fe tyrosine, 304 heme oxidation sensitive bands, 344 isomers of etioporphyrins, 325 ligand of hemes, 338, 339, 340 lipids, 198, 199,204,205 low frequency bands of heme, 341 metal ligand, 311 metal ligand bonds of different metalloproteins, 374 nucleic acids, 138-140, 142, 143, 154, 158, 161 0-0 stretching, 300 rhodopsin, 274-277

448

Index

side chain of hemes, 323 tyrosine, 87 Vibrational circular dichroism (V eo), 58, 59 Vibrational modes, hemes, 317 Vibrational quantum level, 5, 8, 17 Vibronic coupling, 319 Vinyl groups, 322-324 Virtual state, 8, 16, 17 Viruses, 174-182 Visual axis, 397, 398 Visual pigment, 270-283 Vitamin A, 272 Vitamin BJl, 57, 387 Wagging vibration, 31, 204. 274

Wavelength, definition, 4 Wave number, definition, 4

Xanthine, 415 Xanthophyll,257 X-ray diffraction data. 46, 70, 73. 75, ' 81-83,85,86,93,108,145,147, 215, 250, 323, 354

Zinc (Zn), 73,122,124,125,127,159 Zincon, 127 Zineb,426 Zn(II)-octaethylporphyrin, 321