Structural and functional differences in H+-ATPases with native and reconstituted inhibitor protein.

Anti F1 antibodies that react with the alpha and beta subunits of the mitochondrial F0-F1 ATPase complex do not interfere with the natural inhibitor protein-ATPase interaction as revealed by inhibitor peptide titration curves. Submitochondrial particles with endogenous or added bound inhibitor protein show differences in immunoprecipitation. Submitochondrial particles which are partially depleted of inhibitor protein gave the same immunoprecipitation curve as the Mg-ATP particle. Anti F1 antibodies induce differential effects in ATP hydrolysis and ATP-Pi exchange. ATP hydrolysis is stimulated in Mg-ATP particles to 200%, while inhibitor depleted and inhibitor reconstituted particles are inhibited by the presence of the antibodies. ATP-Pi exchange is stimulated in inhibitor reconstituted particles and inhibited in Mg-ATP and inhibitor depleted particles. These results suggest that the inhibitor protein when endogenously bound confers a different conformation to the F1-ATPase than that of the F1 ATPase with added bound inhibitor protein.