Changes in the adenine nucleotide and inorganic phosphate content of Escherichia coli F₁-ATPase during ATP synthesis in dimethyl sulphoxide

Escherichia coli F1-ATPase contained 2.9 +/- 0.1 mol of adenine nucleotide and 3.1 +/- 0.3 mol of Pi/mol of enzyme. After preincubation with ATP, the nucleotide and phosphate contents were 5.6 and 6.0 +/- 0.5 mol/mol of enzyme respectively. The F1-ATPase was induced to synthesize ATP in the presence of 30% (v/v) dimethyl sulphoxide (Me2SO). The ATP originated from endogenous bound ADP. The bound adenine nucleotide and Pi contents of the enzyme during the time course of ATP synthesis were investigated by using F1-ATPase which had been preincubated with ATP. We show that the process of ATP synthesis in Me2SO involves (i) an initial rapid loss of nucleotide from the enzyme, the process being facilitated by exogenous Pi, (ii) a rapid loss of Pi from the enzyme, at least in the absence of exogenous Pi, (iii) re-binding of a portion of the lost nucleotide, and (iv) synthesis of ATP from bound ADP and exogenous Pi. It is proposed that transfer of the F1-ATPase to the Me2SO medium induces a change in the conformation of the enzyme to a form favouring ATP synthesis.