A rapid burst preceding the steady‐state rate of H⁺‐transhydrogenase during illumination of chromatophores of Rhodobacter capsulatus

At the onset of illumination of chromatophores there was a burst (t approx. 5 ms) in the rate of the H⁺-transhydrogenase reaction before establishment of the steady-state rate. The burst was suppressed at high pH with a pK _a, of approx. 8.5. The burst and the steady-state rate were inhibited by either (i) a combination of myxothiazol and carbonylcyanide-p-trifluoromethoxyphenylhydrazone, or (ii) NAD⁺ or (iii) dicyclohexylcarbodiimide. The results support a model in which substrate binding to H⁺-transhydrogenase is relatively fast. A subsequent slow step is accelerated by the protonmotive force and a third step, possibly product release, is rate-limiting in steady-state turnover during illumination.