[Reversibility of the proton-potassium pump and synthesis of ATP in E. coli].

E. coli is able to substitute 2H+ from the external medium for one K+ of a cell with the concurrent synthesis of ATP under certain condition. The 2H+/K+ exchange and coupled ATP synthesis are in need of both the essential H+ (around 24 KJ) and the high K+ gradient (10(3) ) directed from a cell to the medium. The reverse pump, cycle is acutuated as well as the direct one merely through an increase of osmolarity in the environmental medium. The reverse process can be blocked by an insignificant increase in external pH or in K+ concentration, by DCCD or by protonophore. The stoichiometry of the entire pump cycle is ATP:2H+:K+.