Proton flow through the intramembrane sector of the ATP synthase complex of bovine heart mitochondria

Abstract

The mechanism of proton translocation across the mitochondrial F 0-F 1 ATP synthase was investigated by studying the electrical behaviour of the intramembrane sector, F 0, of the ATP synthase as well as by studying the role of dithiol groups of F 0 in proton transport. The conductance properties of F 0 were inferred by determining the current-voltage characteristics of inner mitochondrial membrane preparations in which the interaction between F 1 and F 0 had been selectively damaged so as to open F 0 channels. Such a study indicated that open F 0 channels have a gated response to the membrane potential so that proton flow through F 0 is inhibited at membrane potential values below approximately 100 mV, Specific oxidation of dithiol groups to disulphides was obtained by incubating purified, urea-extracted F 0 with diamide. It was found that, following such treatment, F 0 could no longer be reconstituted into an energy-coupled F 0-F 1 ATP synthase, as apparent from the loss of sensitivity to oligomycin of ATP hydrolysis by the reconstituted enzyme. Moreover, it was found that F 1 and/or the oligomycin sensitivity conferring protein protect F 0 essential dithiols from diamide deleterious oxidation.