Kinetics of dark proton efflux in chloroplasts

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The rate constant for dark proton efflux from preilluminated chloroplasts, was found to be proportional to the proton permeability, and inversely proportional to the ‘proton binding capacity’ of the thylakoids (the ratio between bound and free protons). Dark proton efflux was resolved into two kinetically distinct components: a diffusion-mediated process which was predominant below pH 7, and a separate leakage pathway, characterized by linear dependence on the internal to external proton concentration ratio, which was predominant above pH 7. An increased proton-binding capacity accompanied the increased proton permeability associated with this second pathway.