THERMOLUMINESCENCE EVIDENCE FOR LIGHT-INDUCED OXIDATION OF TYROSINE AND HISTIDINE-RESIDUES IN MANGANESE-DEPLETED PHOTOSYSTEM-II PARTICLES

In the thermoluminescence (TL) glow curve of photosystem II, particles depleted of manganese, a tyrosine modifier, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD) abolishes the TL band appearing around -55-degrees-C (TL-55). Addition of a histidine modifier, diethylpyrocarbonate results in the disappearance of the band peaking around -30-degrees-C (TL-30). NBD treatment also abolishes the EPR signal II(fast) of oxidized tyrosine donor, Y(z), and inhibits the electron transport from diphenylcarbazide to 2,6-dichlorophenol-indophenol. It is concluded that the TL-55 and TL-30 bands can be assigned to oxidized tyrosine (Y(z)+) and histidine (His+) residues, respectively, which participate in electron transfer from manganese to the reaction center of chlorophyll, P680+.