Regulation of Electron Transfer in Chromatium vinosum Chromatophores by Intravesicular H+ Concentration

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Abstract
The possibility that electron transfer is regulated by H concentration in the inner space of chromatophores was examined in the chromatophores of Chromatium vinosum. The re-reduction of cytochrome c-555 after illumination was dependent on the pH of the suspending medium; rapid in the alkaline pH range and slow in the acidic range. A clear dependence of the half-time of the re-reduction on the intravesicular pH, estimated by the fluorescence quenching of 9-aminoacridine, was demonstrated. An almost identical dependency of the half-time on the medium pH was found in the presence of carbonylcyanide m-chlorophenylhydrazone (CCCP). The same pH1n were also observed in the presence of valinomycin, nigericin, and valinomycin plus nigericin. The intravesicular H+ concentration, rather than the H concentration gradient across the membrane or the membrane potential, probably regulates the rate of cyclic electron transfer in Chromatium chromatophores. Under the “phosphorylating” conditions, a difference in the level of adenine nucleotides induced the regulation of electron flow. Again, a correlation of the half-reduction time and the internal H+ concentration can be clearly demonstrated. Kinetic analysis of the reduction of cytochrome c-555 indicated the presence of two electron-donating pools. The rapid electron donation was pH-sensitive and the slower electron donation from a large secondary pool was pH-insensitive and probably diffusion-controlled.