Enzyme catalyzed hydrolysis of inorganic pyrophosphate. Current view of problems in characterization of PP1-phosphohydrolytic activity associated with alkaline phosphatases (EC 3.1.3.1).

A survey of the hydrolytic activity of alkaline phosphatase (EC 3.1.3.1) reveals that PP1, like phosphomonoesters, can serve as substrate in vitro. This pp1-phosphohydrolytic activity can be distinguished from PP1-phosphohydrolytic activities of inorganic pyrophosphatases (EC 3.6.1.1) and glucose-6-phosphatase (EC 3.1.3.9) by several criteria. Discrimination among these hydrolytic enzymes is possible by their dependence on variation of pH and of magnesium to PP1 ratios in the assay solutions. The true substrates and modifiers are not simply PP1 and magnesium, but the equilibrium species in mixtures of these two. The physiological significance of each of the three enzymes is not predictable from their differential efficiency as catalysts of PP1-hydrolysis in vitro.