The pathway of cyclic electron transport in chromatophores of Chromatium vinosum. Evidence for a Q-cycle mechanism

Abstract

Chromatophores of the purple sulfur bacterium Chromatium vinosum were shown to contain a cytochrome similar to cytochrome c 1 and two b cytochromes. Cytochrome b can be accumulated in the reduced form upon illumination at an ambient redox potential of +415 mV in the presence of the electron transport inhibitors antimycin A or HOQNO. The reductions of cytochrome b, of the high-potential cytochrome c 555 and of the primary electron donor P-870 are all inhibited by myxothiazol. Dark-adapted C. vinosum chromatophores show little cytochrome b reduction on the first flash. Considerable cytochrome b reduction (1 cytochrome b:8 P-870 present) is observed on the second flash. This observation and the 1:1 stoichiometry observed between cytochrome b reduction and P-870 + reduction after the second flash support a Q-cycle model for cyclic electron flow in C. vinosum.