The research will focus on the terminal reactions of mitochondrial oxidative phosphorylation dealing with the utilization of the electrochemical proton gradient for the phosphorylation of ADP. The process is carried out by a vesicular H+-ATPase consisting of a hydrophobic membrane-embedded segment (Fo) and a hydrophilic, extrinsic multiprotein complex, F1-ATPase. Among the proteins of Fo is a 15,000 dalton, dithiol protein (coupling factor B or FB) which is essential for vectorial H+ translocation in Fo-F1. In its absence or when it is inhibited, the H+ release appears to be scalar, and ATP synthesis and the reverse H+ pumping reaction is blocked. Thus, detailed knowledge of the properties of FB and its mechanism of action are of crucial importance to a full understanding of one of the last unresolved major problems in metabolism. The aims include determination of the primary structure of FB by the cDNA cloning method, identification of proteins homologous with FB in the H+-ATPase preparations of other species, identification of the nearest neighbor proteins of FB, identification of another thiol protein involved in H+ conduction in Fo, and study of the mechanism of H+ conduction in Fo.