High-light-induced superoxide anion radical formation in cytochrome b<sub>6</sub>f complex from spinach as detected by EPR spectroscopy

Abstract

The generation of superoxide anion radical (O2 .-) in the cytochrome b 6 f complex (Cyt b 6 f) 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 b 6 f 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 b 6 f complex by antioxidants is discussed.