Abstract
ATP synthase (F-ATPase) of chloroplasts, CF 0CF 1, is both activated and driven by transmembrane protonmotive force. We dichotomized between activating and driving proton transfer by specific inhibitors, tentoxin and venturicidin. Thylakoids membranes were submitted to voltage steps (by flashing light) superimposed to a steady pH-difference. Transient proton intake, transfer and release by CF 0CF 1 was monitored by spectroscopic probes. Both activities, activation and catalysis, required all three partial reactions of the proton, however, activating proton transfer rose first (monophasically, τ 1 2 ∼15 ms ) followed by another phase of equal magnitude with a time lag of about 15 ms. Both types of consecutive proton transfer reactions contribute free energy for ATP synthesis.
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