Effect of Antimycin on Photosynthetic Activities in Chromatophores and Whole Cells of Chromatium vinosum

The inhibitory effects of antimycin on various photosyntheticactivities were investigated with Chromatium vinosum chromatophores. Photophosphorylation and proton uptake under continuous illumination,the slow phase of the flash-induced proton uptake, and re-reductionof flash-oxidized cytochrome C555 and the reaction center bacteriochlorophylldimer were half inhibited at about 5 x 10^–7 M antimycinand almost completely inhibited at about 2 x 10^–5 M. N-Methylphenazoniummethosulfate (100 µM) restored the inhibited activitiesof photophosphorylation and proton uptake to the original levels.These results indicated that antimycin, as it inhibits the cyclicelectron transfer in non-sulfur purple bacteria, inhibits thecyclic electron flow involving cytochrome C555 and hence inhibitsthe photosynthetic activities coupled to the electron flow. On the other hand, antimycin had little inhibitory effect onthe proton release by whole cells of Chromatium under continuousillumination. The ineffectiveness was probably due to the lowpermeability of antimycin to the cell wall of the bacterium. The rapid phase of the proton uptake induced by a single-turnoverflash was not inhibited by antimycin, suggesting that the protonuptake is not closely associated with the electron transferinvolving the antimycin-sensitive site. (Received November 20, 1980; Accepted March 11, 1981)