ATP synthesis catalyzed by the ATP synthase of Escherichia coli reconstituted into liposomes

Abstract

The H(+)-translocating F0F1-ATPase from Escherichia coli (EF0F1) was purified and reconstituted into preformed reverse-phase liposomes prepared from egg yolk phosphatidylcholine/phosphatidic acid. The EF0F1 liposomes were energized by an acid/base transition (pHout = 8.3; pHin = 5.0) and a superimposed K+/valinomycin diffusion potential ([K+]out = 100 mM; [K+]in = 0.6 mM) yielding a maximum rate (turnover number) of ATP synthesis of 27 +/- 8 mol ATP . mol EF0F1(-1) . s-1), i.e. 27 +/- 8 s-1. This reaction was inhibited by NH4Cl or by addition of the F0F1 inhibitor N,N'-dicyclohexylcarbodiimide. The rate of ATP synthesis measured as a function of the phosphate and ADP concentrations, can be described by Michaelis-Menten kinetics with a Km of 0.7 +/- 0.2 mM for phosphate ([ADP] = 200 microM) and a Km of 27 +/- 7 microM for ADP ([phosphate] = 5 mM), respectively.