Abstract
(1) The light-induced membrane potential measured by electrochromism in chromatophores and in intact cells of Rhodobacter capsulatus (formerly called Rhodopseudomonas capsulata) was reduced by about 70% with myxothiazol, but only by about 30% with antimycin. (2) The protonomotive current responsible for membrane potential formation was inhibited by more than 97% with myxothiazol and by approx. 89% with antimycin. It is suggested that the Cyt b c 1 complex can catalyse a limited rate of electron transfer even when the quinol reductase site is completely blocked. (3) Titration with both inhibitors yielded a similar, diodic dependence of the dissipative membrane ionic current on the membrane potential. (4) The observations in (1) can be explained completely by (2) and (3). (5) When added alone, antimycin and low concentrations of uncoupling agent only slightly depressed the light-induced membrane potential in chromatophores, but together they had a marked effect. Synergistic depression of membrane potential was less evident with myxothiazol and uncoupling agent. These observations are explained by (a) the fact that the intrinsic membrane ionic conductance is membrane potential-dependent, but that due to uncoupling agent is membrane potential-independent; (b) photosynthetic (cf. respiratory) control is pronounced in the presence of partial titres of myxothiazol, but is absent in antimycin-treated chromatophores.
Published Version
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