Investigation of the role of the substrate metal ion in the yeast inorganic pyrophosphatase reaction

Abstract

The substrate activities of a series of tripositive metal ion-pyrophosphate complexes with yeast inorganic pyrophosphatase were examined. While the Michaelis constants for these complexes were shown to be between one and two orders of magnitude greater than that of the natural substrate, [Mg(H 2O) 4PP i] 2−, the turnover numbers were in general comparable to that of [Mg(H 2O) 4PP i] 2−. These data suggest that the nature of the metal ion cofactor effects substrate binding but in most cases not catalysis. Thus, the role of the metal ion in catalysis is probably restricted to that of an electron sink.