Isolation, subunit structure and localization of inorganic pyrophosphatase of heart and liver mitochondria

Abstract

A procedure has been developed to isolate separately two forms (I and II) of inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1) from bovine heart mitochondria with specific activities of 250 and 39 IU/mg, respectively. The values of M r for enzymes I and II are about 60 000 and 185 000, respectively. Polyacrylamide gel electrophoresis of pyrophosphatase II in the presence of sodium dodecyl sulfate reveals polypeptides of four types with M r of 28 000 (α), 30 000 (β), 40 000 (γ) and 60 000 (δ). Enzyme I consists of two subunits similar in mass to α and β. When rat heart and liver mitochondria are fractionated with digitonin and Lubrol WX, pyrophosphatase II, but not I, remains bound to inner membrane fragments. The results show that the two forms of the mitochondrial pyrophosphatase, one of which is localized in the inner membrane, differ in subunit structure but have a common catalytic part.