FoF1-ATPase Content in Chromatophores of Rhodospirillum rubrum and Stoichiometry of Oligomycin Binding

Abstract

In the FoF1-ATPase of mammalian and yeast mitochondria, the oligomycin sensitivity conferring protein (OSCP) is one of the subunits of the enzyme complex, and is needed for inhibition of ATP hydrolysis by oligomycin (1). The amino acid sequence of OSCP from beef heart mitochondria is homologous to the amino acid sequence of the δ-subunit of the F1-ATPase from E. coli, 26.4% (2), chloroplasts, 25.3% (3), and Rhodospirillum rubrum, 28.9% (2). However, only R. rubrum is sensitive to oligomycin (4). It has also been shown that R. rubrum F1-ATPase, with the β-subunits substituted with β from E. coli, is not oligomycin sensitive when reconstituted to depleted membranes (5). Thus it is obvious that also the composition of the β-subunit is crucial for oligomycin sensitivity. The homology between the β-subunits from beef heart and the other three sources is (2): E. coli 71.8%, tobacco chloroplast 69.0%, and R. rubrum 76.2%. Both the δ- and the β-subunit of R. rubrum thus show stronger homology with the same sub-units from bovine heart mitochondria than do the subunits from chloroplasts and E. coli.