Tyrosine vibrations

In contrast to the distinct long-wavelength band observed in 1,2-CTD-catechol and 3,4-PCD-protocatechuate spectra (680-720 nm, e= 1700-2500 M cm ) [4, 15, 22, 66], only a broad band at 490 nm (e = 3380 M cm ) is observed after addition of catechol to CCD [100]. The red shift of the broad 425 nm band to -515 nm is also observed by addition of 3,5-dichlorocatechol to CCD [104], indicating the coordination of catecholate to Fe ". The enzyme tyrosine vibrational bands of resonance Raman spectra disappear by addition of catechol, and new bands appear at 1477,1318,1257, and 1148 cm which are... 

Figure 3.35 presents TR spectra obtained with varying time delays between the pump and probe pulses following photolysis of HbCO. The Raman band features have been attributed to tyrosine (Y) and tryptophan (W) vibrational modes as indicated at the top of Figure 3.35. These Raman bands change with time and provide information about the environment of the typrosine and tryptophan residues in the heme. Inspection of Figure 3.35 reveals that the negative difference Raman...

In the resonance Raman spectra of GO0X (125), vibrational modes have been assigned to both the tyrosinate ligand (Tyr 495) as well as the tyrosyl radical (Tyr 272). The spectrum does not provide evidence for the speculation that the tyrosyl radical is delocalized onto the jr-stacked tryptophan residue (Trp 290) (126, 127). Recent results of high-frequency EPR measurement (30) on the apogalactose oxidase radical are also consistent with the radical spin density being localized on the modified Tyr 272 moiety only. 

Ionization of the phenol hydroxyl group in tyrosine shifts the 277-nm absorption peak to 294 nm and the 223-nm peak to 240 nm. The molar extinction coefficient for the peak of the lower energy band increases from about 1350 M l cm-1 to about 2350 M em-1 and for the higher energy band from about 8200 M cm-1 to about. 1,000 M l cm-1.113 141 In addition, the lower energy absorption band of tyrosine shows vibrational structure that is lost upon ionization of the phenol side chain. 

In the case of tyrosine, the sign of the CD bands can be either positive or negative but is the same throughout a given transition. The CD bands are similar in shape to the absorption bands.36 98 The behavior of phenylalanine is more complex. The progression of vibrational subbands at 930 cm-1 intervals above the 0-0 band all have the same sign, and the intensities relative to that of the 0-0 band are similar to those in absorption. However, the vibrations of wave numbers equal to... 

UV resonance Raman spectroscopy (UVRR), Sec. 6.1, has been used to determine the secondary structure of proteins. The strong conformational frequency and cross section dependence of the amide bands indicate that they are sensitive monitors of protein secondary structure. Excitation of the amide bands below 210 nm makes it possible to selectively study the secondary structure, while excitation between 210 and 240 nm selectively enhances aromatic amino acid bands (investigation of tyrosine and tryptophan environments) (Song and Asher, 1989 Wang et al., 1989, Su et al., 1991). Quantitative analysis of the UVRR spectra of a range of proteins showed a linear relation between the non-helical content and a newly characterized amide vibration referred to as amide S, which is found at 1385 cm (Wang et al., 1991). 

Work on indole, tryptophan, etc. continues because of their relevance to the complex field of protein photophysics. Creed has produced reviews of the photophysics and photochemistry of near-u.v.-absorbing amino-acids, viz. tryptophan and its simple derivatives, tyrosine and its simple derivatives, and cysteine and its simple derivatives. The nature of the fluorescent state of methylated indole derivatives has been examined in detail by Meech et al. Another investigation on indole derivatives deals particularly with solvent and temperature effects. Fluorescence quenching of indole by dimethylfor-mamide has also been examined in detail. Fluorescence excitation spectra of indoles and van der Waals complexes by supersonic jets give microscopic solvent shifts of electronic origin and prominent vibrational excitation of L(, states. Conventional flash photolysis of 1-methylindole in water shows R, e p, and a triplet state to be formed. " Changes in the steady-state fluores-... 

The visible spectra of the intradiol dioxygenases (Fig. 2) are characterized by a broad absorption band centered near 460 nm with molar extinction coefficients of 3000-4000 M-1 cm-1 16>34). The color disappears upon reduction of the ferric ion with dithionite and is regenerated upon exposure of the solution to oxygen. Resonance Raman studies on these enzymes15 35-38) have been reported by several laboratories (Table 4). These spectra are characterized by a set of four peaks at ca. 1605, 1505, 1270, and 1175 cm-1, which are assigned to ring vibrations of Fe(III) coordinated tyrosinate ligands. Similar spectra are obtained for the transferrins as well as for model iron-phenolate complexes (Table 4). A new class of iron proteins seems to... 

Table 4. Resonance Raman frequencies of phenolate ring vibrations in iron-tyrosinate proteins and model complexes...

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