The Influence of the Ionic Conductance on the Relation between Electron Transport and Proton‐Motive Force in Intact Cells of Rhodopseudomonas capsulata

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Abstract
The dependence of membrane potential (.DELTA..psi.) on the rate of respiration in darkened intact cell suspensions of R. capsulata was distinctly non-linear; severe inhibition of respiration with rotenone or KCN led to only a small drop in .DELTA..psi.. In the presence of 0.3 .mu.M carbonylcyanide p-trifluoromethoxyphenylhydrazone [CF3OPhzC(CN)2] the dependence of .DELTA..psi. on respiratory rate became linear. Consequently and particularly at lower concentrations of CF3OPhzC(CN)2, there was a pronounced synergistic depression of the respiratory .DELTA..psi. with CF3OPhzC(CN)2 and rotenone or KCN. Antimycin A, at a concentration which strongly inhibited the photosynthetic electron transport chain, only slightly lowered the light-induced .DELTA..psi. in anaerobic cell suspensions. Antimycin and CF3OPhzC(CN)2 synergistically lowered .DELTA..psi. generated by illumination. The light-induced .DELTA..psi. in anaerobic cells was only about 1.5-times larger than the respiratory-induced .DELTA..psi. in darkened cells. It required approximately 16-times more CF3OPhzC(CN)2 to collapse the photosynthetic .DELTA..psi. than the respiratory .DELTA..psi.. These results are discussed with reference to an ionic current/.DELTA..psi. relation. The unifying feature is that the intrinsic conductance of the cell membrane is strongly dependent on .DELTA..psi., but the conductance due to CF3OPhzC(CN)2 is independent of .DELTA..psi.