Bacterial protein translocation: kinetic and thermodynamic role of ATP and the protonmotive force.

The energetic mechanism of preprotein export in Escherichia coli has been a source of controversy for many years. In vitro studies of translocation reactions that use purified soluble and membrane components have not clarified the main features of this mechanism. Translocation occurs through consecutive steps which each have distinct energy requirements. Initiation of translocation requires ATP and the SecA protein. Most of the further steps can be driven by the protonmotive force (delta p).