H+-pumping ATPase has little stimulatory effect on in Vitro translocation of a model protein into Vibrio alginolyticus inside-out membrane vesicles

Abstract

We studied the effect of a H+ electrochemical potential generated by F1F0 ATPase on in vitro translocation of a model protein into Vibrio alginolyticus inside-out membrane vesicles. The F1F0 ATPase of V. alginolyticus catalyzed the pumping of H+ coupled to ATP hydrolysis as measured in fluorescence quenching experiments. Consequently, this enzyme leads to the generation of a H+ electrochemical potential. The H+ electrochemical potential generated by F1F0 ATPase was completely abolished by 30 μM N,N′-dicyclohexylcarbodiimide (DCCD) or 5 μM carbonylcyanide m-chlorophenylhydrazone (CCCP) at 30 °C. The treatment of membrane vesicles with 30 μM DCCD at 30 °C had little influence on the translocation activity of uncleavable OmpF-Lpp, a model secretory protein, as compared to the intact membrane vesicles. On the other hand, the NADH:quinone oxidoreductase of V. alginolyticus is known to be a Na+ pump that leads to generation of a Na+ electrochemical potential. This Na+ electrochemical potential stimulates protein translocation into inside-out membrane vesicles prepared from V. alginolyticus in the presence of Escherichia coli SecA [Tokuda, H., Kim, Y. J., and Mizushima, S. (1990) FEBS Lett. 264, 10-12] From these results, it is evident that the stimulatory effect of the Na+ electrochemical potential on protein translocation in V. alginolyticus is not affected by the H+ electrochemical potential influence of F1F0 ATPase.