Reduction of plastocyanin with O2- and superoxide dismutase-dependent oxidation of plastocyanin by H2O2.

Type I copper proteins, plastocyanin and rice blue protein, were reduced with O2 (-). The reduction rate constants of plastocyanins from several sources with O2 (-) are about 10(6) m(-1) sec(-1) (1.0 × 10(6) m(-1) sec(-1) for spinach and kidney bean plastocyanins and 6.7 × 10(5) m(-1)sec(-1) for Japanese radish plastocyanin) at pH 7.8 at 25°C and not significantly different from that observed for rice blue protein (7.3 × 10(5) m(-1)sec(-1)). Reduced plastocyanin was oxidized by H2O2 through the peroxidase-like reaction of Cu,Zn-superoxide dismutase.