The generation of superoxide anion radical (O2.-) in the cytochrome b6f complex (Cyt b6f) of spinach under high-light illumination was studied using electron paramagnetic resonance spectroscopy. The generation of O2.- was lost in the absence of molecular oxygen. It was also suppressed in the presence of NaN3 and could be scavenged by extraneous antioxidants such as ascorbate, β-carotene, and glutathione. The results also indicate that O2.-, which is produced under high-light illumination of the Cyt b6f from spinach, might be generated from a reaction involing 1O2, and the Rieske Fe-S protein could serve as the electron donor in the O2.- production. The mechanism of photoprotection of the Cyt b6f complex by antioxidants is discussed. and M. Sang ... [et al.].
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., A. A. Khorobrykh, D. V. Yanykin, V. V. Klimov., and Obsahuje bibliografické odkazy