501—An electrochemical study of energy-dependent potassium accumulation in E. coli: Part IX. Reversal of the mechanism exchanging 2 H + for K + with the coupled synthesis of ATP

Abstract

E. coli is able to exchange 2 H + from the external medium for one K + of a cell with the concurrent synthesis of ATP. The 2 H +/K + exchange and the coupled ATP synthesis are in need of both the essential Δ \\ ̃ gm H+ (around 24 kJ) and the high K + gradient (10 3) directed from a cell to the medium. The reverse pump cycle is actuated as well as the direct one [3] merely through an increase of osmolarity in the environmental medium. The reverse process can be blocked by the insignificant ncrease in external pH or in K + concentration, as well as by DCCD or by protonophore. The stoichiometry of the entire pump cycle is ATP: 2 H + :K +. These observations, as well as the previous findings [8,9] that 2 H + from a cell and one external K + are transported through F 1·F 0 and TrkA respectively, suggest that F 1·F 0 and TrkA form the structural association in bacterial membrane for the joint employment of phosphate bond energy, the supercomplex (F 1 ·F 0TrkA operating as an electrogenic proton-potassium pump with stable stoichiometry ATP:2 H + :K +.