ATP synthase: Driven and activated by protonmotive force

ATP synthase (F‐ATPase) of chloroplasts, CF 0 CF 1 , is both activated and driven by transmembtane protonmotive force. We dichotomized between activating and driving proton transfer by specific inhibitors, tentoxin and venturicidin. Thylakoid membranes were submitted to voltage steps (by flashing light) that were superimposed to a steady pH‐difference. Transient proton uptake, transfer and release by CF 0 CF 1 were studied by spectroscopic probes. Both, activation and catalysis required all three partial reactions of the proton. A fast electrogenic reaction preceded the catalytic turnover of CF 0 CF 1 . This activating electrogenic event in response to the rapid onset of the electric potential is an integral portion of the reaction sequence producing ATP.