ATP synthesis and hydrolysis by a hybrid system reconstituted from the beta-subunit of Escherichia coli F1-ATPase and beta-less chromatophores of Rhodospirillum rubrum.

Photophosphorylation and ATPase activities were restored to beta-less Rhodospirillum rubrum chromatophores by their reconstitution with purified beta-subunits of either R. rubrum F1-ATPase (Rr beta) or Escherichia coli F1-ATPase (Ec beta). In the homologous reconstituted system both activities were restored to the same extent, whereas in the hybrid system ATP synthesis was restored to about 10% when the hydrolysis was restored to 200%. This difference in rates of synthesis and hydrolysis was not due to any general uncoupling effect of Ec beta leading to an increased membrane permeability to protons, because with both hybrid and homologous systems an identical light-induced quenching of quinacrine fluorescence was observed. They differed, however, in ATP-driven quenching of quinacrine fluorescence, which was much lower in the hybrid system. These results suggest that the hybrid has a decreased capacity for proton-translocation through the membrane-bound Fo channel during ATP hydrolysis, and probably also during ATP synthesis. The very high ATPase activity of the hybrid system indicates that it might enable the released protons to leak to the outside medium rather than to move inside through the Fo channel. The activities restored by Rr beta and Ec beta exhibit a similar sensitivity to dicyclohexylcarbodiimide, but different sensitivities to oligomycin and to an anti-E. coli F1 (EcF1) antibody. Oligomycin inhibited only the homologous R. rubrum system whereas anti-EcF1 was a much more effective inhibitor of the hybrid system. It is therefore concluded that Rr beta plays a role, that the Ec beta cannot fulfill, in conferring oligomycin sensitivity to the RrFo X F1-ATP synthase-ATPase complex.