The rate of ATP synthesized by the ATP synthase (F,,F,-ATPase) is limited by the rate of energy production via the respiratory chain, when measured in everted membrane vesicles of an Eschericliia coli atp wild-type strain. After energization of the membranes with NADH, fractional inactivation of F,,F, by the covalent inhibitor N,N'-dicyclohexylcarbodiimide allowed the rate of ATP synthedmol remaining active ATP synthase complexes to increase ; the active ATP synthase complexes were calculated using ATP hydrolysis rates as the defining parameter. In addition, variation of the assay temperature revealed an increase of the ATP synthesis rate up to a temperature of 37"C, the optimal growth temperature of E. coli. In parallel, the amount of F,,F, complexes present in membrane vesicles was determined by immnnoquantitation to be 3.3 t 0.3 % of the membrane protein for cells grown in rich medium and 6.6 t 0.3 % for cells grown in minimal medium with glycerol as sole carbon and energy source. Based on these data, a turnover number for ATP synthesis of 270 5 40 s~' could be determined in the presence of 5 8 active F,F, complexes. Therefore, these studies demonstrate that the ATP synthase complex of E. coli has, with respect to maximum rates, the same capacity as the corresponding enzymes of eukaryotic organells.Keywords: F,,F, ATP synthase ; oxidative phosphorylation ; turnover number; dicyclohexylcarbodiimide :
Escherichia coli.ATP synthases (F,F,-ATPases) are found in energy-transducing membranes of mitochondria, chloroplasts and bacteria, where they catalyze the synthesis of ATP from ADP and inorganic phosphate using an electrochemical gradient of protons built up by respiration or photosynthesis. In bacteria. the enzyme can also function in the reverse direction by coupling the hydrolysis of ATP to the translocation of protons. The multisubunit enzyme complex consists of the globular, water-soluble F, complex and the membrane-integrated F, complex linked by a stalk. The F, complex carries the catalytic sites for ATP synthesis and hydrolysis, whereas the F,, complex constitutes a path for protons across the membrane. Energy released by proton translocation through F,, is relayed to the catalytic sites in F, by conformational changes. In Escherichia coli, the F, complex is composed of the three different polypeptides a, b, and c in a stoichiometry of 1 : 2: 10 t 1, whereas the F, complex consists of five subunits with a stoichiometry of a&& (Fillingame, 1990, 1992: Capaldi et al., 1994Deckers-Hebestreit and Altendorf, 1996). Recently, the F, part of bovine heart mitochondria was crystallized and the structures of the subunits a, / l , and part of 7 , have been solved by X-ray diffraction at 0.28-nm resolution (Abrahams et al., 1994).F,F,-ATPases from different sources reveal great similarities in subunit composition, structure and function. Hence, one could Enzyme. ATP synthase (F,,F,) (EC 3.6.1.34).Bertani; SMP, submitochondrial particles.imply that also the catalytic mechanisms and the turnover numbers of the enzyme c...