Roles of H+-ATPase and proton motive force in ATP-dependent protein translocation in vitro.

Membrane vesicles from an Escherichia coli mutant with a deletion of the uncBC operon required ATP to translocate proteins, thus ruling out an essential role of F1F0-H+-ATPase in ATP-dependent protein translocation. Moreover, proteins could be translocated in the absence of proton motive force. At suboptimal ATP concentrations, D-lactate stimulated protein translocation, indicating that proton motive force, although insufficient to support translocation, could facilitate the process.