INHIBITORS OF PHOTOPHOSPHORYLATION AND PHOTOREDUCTION BY CHROMATOPHORES FROM RHODOSPIRILLUM RUBRUM

Dio-9 and phlorizin have been found to inhibit to the same extent the endogenous phosphorylation, the ascorbate-indophenol supported phosphorylation and the phenazine methosulfate supported phosphorylation by Rhodospirillum rubrum chromatophores. The succinate-linked NAD+ photoreduction was blocked by Dio-9 to the same degree as the photophosphorylation, unlike the case of oligomycin. Tetrabromo-2-trifluoromethyl benzimidazole was found to inhibit NAD+ photoreduction even more than the phosphorylation. This compound was also more effective in blocking both the endogenous and the ascorbate-indophenol mediated phosphorylation than the phenazine methosulfate-supported phosphorylation, which required tenfold higher concentrations of the inhibitor. Differences in the sensitivity of the three systems of phosphorylation towards 2-n-heptyl-4-hydroxyquinoline N-oxide were also observed. These results suggest that the by-pass of the 2-n-heptyl-4-hydroxyquinoline N-oxide-sensitive site in the endogenous system which is mediated by phenazine methosulfate is different and probably shorter than the ascorbate-indophenol induced by-pass. © 1969.