Turnover number of Escherichia coli F0F1 ATP synthase for ATP synthesis in membrane vesicles

Abstract

The rate of ATP synthesized by the ATP synthase (F0F1-ATPase) is limited by the rate of energy production via the respiratory chain, when measured in everted membrane vesicles of an Escherichia coli atp wild-type strain. After energization of the membranes with NADH, fractional inactivation of F0F1 by the covalent inhibitor N,N'-dicyclohexylcarbodiimide allowed the rate of ATP synthesis/mol 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 degrees C, the optimal growth temperature of E. coli. In parallel, the amount of F0F1 complexes present in membrane vesicles was determined by immunoquantitation to be 3.3 /- 0.3% of the membrane protein for cells grown in rich medium and 6.6 /- 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 /- 40 s(-1) could be determined in the presence of 5% active F0F1 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.