Protonmotive force as the source of energy for adenosine 5' triphosphate synthesis in Escherichia coli

Net synthesis of adenosine 5' triphosphate (ATP) in energy depleted cells of E. coli was observed when an inwardly directed protonmotive force was artificially imposed. In wild type cells, ATP synthesis occurred whether the protonmotive force was dominated by the membrane potential (negative inside) or the pH gradient (alkaline inside). Formation of ATP did not occur unless the protonmotive force exceeded a value of 200 mV. Under these conditions, no ATP synthesis was found when cells were exposed to an inhibitor of the membranebound Ca²+ and Mg²⁺ stimulated adenosine triphosphatase (EC 3.6.1.3), dicyclohexylcarbodiimide, or to a proton conductor, carbonylcyanide p trifluoromethoxyphenyl hydrazone. Adenosine triphosphatase negative mutants failed to show ATP synthesis in response to either a membrane potential or a pH gradient. ATP synthesis driven by a protonmotive force was observed in a cytochrome deficient mutant.