Tyrosine photo-activated

Andreev OA, Reshetnyak Y, Goldfarb RH. Evidence of inter- and intra-molecular crosslinking of tyrosine residues of carmodulin induced by photo-activation of ruthenium(II). Photochem Photobiol Sci 2002 1 834-6. 

Fig. 3.2a Electron transport in (natural) photosynthesis. P = chlorophyll that acts as a light sensitizer, from which a photogenerated electron travels to Q = Plastquinone that in combination with CO2 forms a carbohydrate. The photo-ejected electron from Peso is replenished by taking one from the Mn cluster through the redox active tyrosine linkage (or mediator), which in turn extracts an electron from water.

Oxidation. The side chains of cysteine (Cys), histidine (His), methionine (Met), tryptophan (Trp), and tyrosine (Tyr) residues are susceptible to oxidation. Oxidation can result in loss of protein activity. Met is the most reactive residue, oxidizing even with atmospheric oxygen to form Met-sulfoxide, which is frequently observed in proteins (Fig. 135). Additional sources of oxidation include oxidizing agents (peroxides in excipients), metal-catalyzed oxidation and photo-oxidation. Oxidation can be detected... 

The modification of histidine residues and tyrosine residues produces a similar, and interesting, change in the enzyme activity. Photo-oxygenation of the 40 histidine residues in aldolase, sensitized by Rose Bengal, results in the modification of approximately one-half of the imidazole rings [47]. The activity is reduced to a small fraction of its initial value by this operation. The modified enzyme can still form the imine with substrate, and in fact has little change in the rate of cleavage of fructose... 

Figure 6a shows the aromatic part of the 360 MHz spectrum of bovine pancreatic rlbonuclease A (1.5 idH In D2O, pH 7.0, 38%). The spectral resolution was artificially enhanced by multiplication of the FID by a sine bell (HOthrlch et al., 1977). The spectrum of RNase S Is very similar. The doublet resonances of three of the six tyrosine residues Indicated by Yl, Y2, and Y3 have been Indentlfled by double resonance methodes (Lenstra et al., 1978). The photo-CIDNP difference spectra of RNase A and RNase S taken under the same conditions are shown In Figure 6b and 6c. Positively enhanced lines at 7.92 ppm and 6.71 ppm belong to the C-2 and C-4 protons of His 119. This active site residue Is also the most exposed of the four histidines as judged from the X-ray structure (Richards and Wyckoff, 1971) For RNase A (figure 6b)... 

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