High-light-induced superoxide anion radical formation in cytochrome b f complex from spinach as detected by EPR spectroscopy.

The generation of superoxide anion radical (O) in the cytochrome b f complex (Cyt b f) of spinach under high-light illumination was studied using electron paramagnetic resonance spectroscopy. The generation of O was lost in the absence of molecular oxygen. It was also suppressed in the presence of NaN and could be scavenged by extraneous antioxidants such as ascorbate, β-carotene, and glutathione. The results also indicate that O, which is produced under high-light illumination of the Cyt b f from spinach, might be generated from a reaction involing O, and the Rieske Fe-S protein could serve as the electron donor in the O production. The mechanism of photoprotection of the Cyt b f complex by antioxidants is discussed. [ABSTRACT FROM AUTHOR]