Both ATP and the electrochemical potential are required for optimal assembly of pro-OmpA into Escherichia coli inner membrane vesicles.

Pro-OmpA is processed to OmpA by isolated inverted plasma membrane vesicles from Escherichia coli. In the presence of ATP and a membrane potential, 58% (+/- 13%) of the OmpA is sequestered in the vesicles. We sought to determine which of these two metabolic energy sources is used for protein translocation. The plasma membrane F1F0-ATPase is the central enzyme that interconverts the energy of membrane electrochemical potential and ATP. To separate the effects of these two forms of energy in vitro, the ATPase was inactivated, either by "stripping" the F1 from the membranes with low salt and EDTA or by using membrane vesicles derived from a strain without the atp operon. In each case, optimal translocation and processing of pro-OmpA required both a membrane potential and ATP. We conclude that ATP and membrane potential are separate requirements for bacterial protein export.