Components and mechanism of action of ATP-driven proton pomps

Abstract

Compositions of ATP-driven proton pumps from bovine heart mitochondria were studied and the oligomycin-sensitive ATPase complex was reconstituted from its individual components. The complex contains 9 to 10 subunits of which 5 are assembled in the soluble F1 protein, 2 are required for attachment of F1 to the membrane and 2 form the proton channel within the membrane. With the help of information obtained from studies of the chloroplast and the bacterial proton pumps, a function was tentatively assigned to each subunit of the pump. The position of F1 outside of the membrane seen in EM of negatively stained preparations does not appear to be an artifact. Evidence from immunological studies, chemical derivatizations and further EM (positive staining and freeze-etching), support this statement. In this paper a 28,000-dalton polypeptide is described which was isolated from the mitochondria membrane and is required for the reconstitution of oligomycin-sensitive ATPase and 32Pi-ATP exchange activity. A mechanism of action of the proton pump in which the key energy-yielding reaction is the binding of Mg2+ to the protein is proposed. The function of the proton gradient is to displace Mg2+ from this site to permit cyclic repetition of the binding process. Essential for this scheme is the cyclic opening and closing of the proton channel. Present approaches to test this hypothesis are outlined.