The Pyruvate-Phosphate Dikinase Reaction

An enzyme capable of catalyzing the reaction AMP + PPi + P-enolpyruvate ⇌ ATP + Pi + pyruvate was obtained from Bacteroides symbiosus cell extracts and was purified from interfering enzyme activities. It was strongly stimulated by ammonium ion. In this respect and in other physical properties the bacterial enzyme differed from that previously obtained from Entamoeba histolytica. In a complete reaction system the enzyme transferred label from orthophosphate to pyrophosphate and to the γ position of ATP while the label of 32P-enolpyruvate was transferred to the β position of ATP. The observed equilibrium constant catalyzed by the bacterial enzyme was directly dependent upon the square of the hydrogen ion concentration. At pH 7.0 its value was 1140. Apparent Km values for P-enolpyruvate and pyrophosphate were 0.07 mm and 0.1 mm for the amebal enzyme and 0.06 mm and 0.1 mm for the bacterial enzyme, respectively.