Effects of monofunctional sulfhydryl reagents on the proton permeability of pea thylakoid membranes

Abstract

The effects of dark and light labeling of the sulfhydryl groups within the CF i complex with monofunctional maleimides on the dark proton efflux from pea chloroplasts have been studied by measuring the kinetics decay of the proton gradient in the dark. It was found that the steady-state value of the light-induced proton gradient (ΔpH) under nonphosphorylating conditions markedly decreases when both NEM and SLM bind light accessible thiol groups, even at very low (10 μM) maleimide concentrations. Concomitant with this was a considerable increase of the decay rate constant k d of the dark proton leakage. Resolving non-coupled proton efflux mediated by CF 1 complex from the passive proton diffusion on a kinetic basis, it is suggested that the increased dark proton efflux could be attributed to the stimulation of proton permeability through the CF 1 complex.