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 · molEF0F1−1· 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 μM) and a Km, of 27±7 μM for ADP ([phosphate] = 5 mM), respectively. Copyright © 1994, Wiley Blackwell. All rights reserved