Oxidation-reduction potential dependence of pyrophosphate-induced cytochrome and bacteriochlorophyll reactions in Rhodospirillum rubrum

The oxidation-reduction potential dependence of pyrophosphate-induced reactions in chromatophores from the blue-green mutant of Rhodospirillum rubrum has been studied. Two types of energy-requiring reactions are apparent: (1) Absorption changes resulting from bacteriochlorophyll interaction with a high energy state within the membrane. This reaction is independent of the oxidation-reduction potential poise between −475 mV and +430 mV; the reaction is attenuated from +430 mV to 530 mV as the bacteriochlorophyll is chemically bleached. (2) Oxidation-reduction reactions of cytochrome b ( λ max 562–563 nm; E m7.0 − 105 mV) and a cytochrome c ( λ max 552–553 nm; E m7.0 + 295 mV). Antimycin A abolishes the pyrophosphate-induced cytochrome oxidation-reductions but not the bacteriochlorophyll reactions, whereas uncoupler abolishes both cytochrome and bacteriochlorophyll reactions.