Adenosine Triphosphate Conservation in Biosynthetic Regulation

Phosphoribosylpyrophosphate synthase (EC 2.7.6.1.) from Escherichia coli is inhibited by adenosine diphosphate and to a much smaller extent by other nucleotides and by tryptophan. We propose (a) that the adenosine diphosphate effect is part of a general adenosine triphosphate conservation system that causes the rate of expenditure of ATP to be sharply curtailed when the energy charge of the cell decreases slightly; and (b) that, as appears to be the case with phosphoribosyl-pyrophosphate synthase, such ATP conservation control may be superposed on product negative feedback regulation of the same enzyme.