Studies on inorganic pyrophosphatase using imidodiphosphate as a substrate.

Baker's yeast inorganic pyrophosphatase has been found to catalyze Mg2+-dependent hydrolysis of imidodiphosphate yielding phosphate and amidophosphate. The reaction proceeds linearly in the presteady state. The catalytic constant is maximal at pH 9.0 and equals 0.5 min-1. Kinetic titrations of the enzyme with imidodiphosphate and Mg2+ have provided direct evidence for the involvement of three Mg2+ per active site in the transition state of the pyrophosphatase reaction.