Photooxidation and photoreduction of exogenous cytochrome c by photosystem II preparations after various modifications of the water-oxidizing complex
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The redox interaction of exogenous cytochrome c550 (Cyt) with PSII isolated from spinach was studied. Illumination of PSII particles in the presence of Cyt led to: (1) Cyt photooxidation by PSII reaction center (demonstrated at the first time), (2) Cyt photoreduction via O2−• photoproduced on the acceptor side of PSII, and (3) Cyt photoreduction by reduced electron carriers of PSII. A step-by-step removal of components of water-oxidizing complex was accompanied by the appearance of Cyt photooxidation, an increase in the superoxide dismutase (SOD)-dependent Cyt photoreduction (related to O2−• formation), and a decrease in the SOD-independent Cyt photoreduction. Re-addition of PsbO protein diminished the Cyt-induced restoration of electron transfer in PSII. Addition of diuron led to inhibition of these photoprocesses, while exogenous Mn2+ inhibited only the Cyt c photooxidation. The results can be important for correct measurements of O2−• photoproduction in PSII and for elucidation of the role of cytochrome c550 in cyanobacterial PSII.
Additional key wordscytochrome c photooxidation photoreduction photosystem II superoxide anion radical
the primary electron donor of PSII
pheophytin (the primary electron acceptor of PSII)
redox active tyrosine residue 161 of D1 protein
photoinduced changes of chlorophyll fluorescence yield of PSII
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