A rapid burst preceding the steady-state rate of H(+)-transhydrogenase during illumination of chromatophores of Rhodobacter capsulatus. Implications for the mechanism of interaction between protonmotive force and enzyme.
At the onset of illumination of chromatophores there was a burst (t1/2 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 pKa 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.
Palmer
T
T
School of Biochemistry, University of Birmingham, UK.
Jackson
J B
JB
D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D008564:Membrane Potentials; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009250:NADP Transhydrogenases / Q000378:metabolism*; D010788:Photosynthesis; D016354:Rhodobacter capsulatus / Q000378:metabolism*
D009243:NAD; D009249:NADP; D009250:NADP Transhydrogenases