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

The inhibitory effects of antimycin on various photosynthetic activities were investigated with Chromatium vinosum chromatophores. Photophosphorylation and proton uptake under continuous illumination, the slow phase of the flash-induced proton uptake, and re-reduction of flash-oxidized cytochrome C555 and the reaction center bacteriochlorophyll dimer were half inhibited at about 5 × 10−7M antimycin and almost completely inhibited at about 2 × 10−5M. N-Methylphenazonium methosulfate (100 μM) restored the inhibited activities of photophosphorylation and proton uptake to the original levels. These results indicated that antimycin, as it inhibits the cyclic electron transfer in non-sulfur purple bacteria, inhibits the cyclic electron flow involving cytochrome C555 and hence inhibits the photosynthetic activities coupled to the electron flow. On the other hand, antimycin had little inhibitory effect on the proton release by whole cells of Chromatium under continuous illumination. The ineffectiveness was probably due to the low permeability of antimycin to the cell wall of the bacterium. The rapid phase of the proton uptake induced by a single-turnover flash was not inhibited by antimycin, suggesting that the proton uptake is not closely associated with the electron transfer involving the antimycin-sensitive site.