Purification and some properties of a neutral muscle pyrophosphatase

In the water-soluble fraction of rabbit skeletal muscle, at least two types of inorganic pyro phosphatase (PPase) are distinguishable on ion exchange column chromatography. One of them, pyrophosphatase-A (PPase-A), was isolated in an electrophoretically homogeneous form. This enzyme catalyzed the hydrolysis of PPi but not that of other phosphate esters. Only Mg2+ was required for activity and stability. Other cations such as Ca2+, Co2+, Mn2+, and Zn2+ had no activating effect. The activity of this PPase was optimum at pH 7.4. ATP, ADP, sodium imidodiphosphate (PNP), p-chloromercuribenzoate, and Ca2+ inhibited its enzymic activity. The enzyme was protected by dithiothreitol (DTT) against heat denaturation. The molecular weight was estimated to be 67,000 by gel filtration and the molecular size of the subunit was found to be 35,000 by gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). The enzyme probably consists of two identical subunits of 35,000 daltons.