Interaction between the Respiratory and Photosynthetic Electron Transport Chains of Intact Cells of Rhodopseudomonas capsulata Mediated by Membrane Potential

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Abstract
The inhibition of respiration by light and the relief from the inhibition by uncoupling agents were studied in intact cells of R. capsulata. The same concentration range of carbonylcyanide p-trifluoromethoxyphenylhydrazone [CF3OPhzC(CN)2] prevented light-inhibition of respiration and depressed the membrane potential (.DELTA..psi.) in illuminated, aerobic bacterial suspensions. For a wide range of CF3OPhzC(CN)2 concentration the dependence of the respiration rate on .DELTA..psi. in darkened cells coincided with that in illuminated cells. When present separately, antimycin A and low concentrations of CF3OPhzC(CN)2 had little effect on light-inhibition of respiration or on .DELTA..psi. in illuminated, aerobic cells, but added together they gave relief from light-inhibition and they lowered .DELTA..psi.. In the absence of CF3OPhzC(CN)2 even very low light intensities were sufficient to inhibit respiration and increase .DELTA..psi.. In the presence of CF3OPhzC(CN)2 much higher light intensities were necessary. The results are interpreted as evidence that light-inhibition of respiration is mediated by .DELTA..psi.. The modification of the response by uncouplers, inhibitors and with light intensity is critically determined by the ionic conductance properties of the membrane.

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