Incubation of highly purified Escherichia coli succinic thiokinase (succinate: coenzyme A ligase (adenosine diphosphate), EC 220.127.116.11) and the coenzyme A analog, desulfo-coenzyme A, with succinate, adenosine triphosphate, and Mg2+ resulted in stimulation of succinyl phosphate synthesis. This suggests that coenzyme A is required for optimal formation of enzyme-bound succinyl phosphate. The Km of desulfo-coenzyme A in this reaction was 6.2 × 10-5 M. A virtually absent ATPase activity of the enzyme was significantly stimulated by both coenzyme A and desulfo-coenzyme A. The Km of desulfo-coenzyme A in this reaction was 1.4 × 10-3 M. The possible significance of these results is discussed. During these studies it was found that succinyl phosphate is converted nonenzymatically into succinamic acid in the presence of (NH4)2SO4 at pH 7.2.
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