Reduction of cytochrome b-561 through the antimycin-sensitive site of the ubiquinol-cytochrome c2 oxidoreductase complex of Rhodopseudomonas sphaeroides

Cytochrome b-561 of the ubiquinol-cytochrome c 2 oxidoreductase complex of Rhodopseudomonas sphaeroides is reduced after flash illumination in the presence of myxothiazol in an antimycin-sensitive reaction. Flash-induced reduction was observed over the redox range in which cytochrome b-561 and the Q-pool are both oxidized before the flash. The extent of reduction increased with increasing pH, and was maximal at pH > 10.0 where the extent approached that observed in the presence of antimycin following a group of flashes. Reduction of cytochrome b-561 in the presence of myxothiazol showed a lag of ~ 1 ms after the flash, followed by reduction with ( t 1 2 ~ 6 ms; by analogy with the similar kinetics of the quinol oxidase site, we suggest that the rate is determined by collision with the QH 2 produced in the pool on flash excitation.