Characterization and purification of a calcium-sensitive ATP diphosphohydrolase from pig pancreas

An ATP diphosphohydrolase (EC 3.6.1.5) from the pancreas of the pig has been characterized and purified. The enzyme which has an optimum pH between 8 and 9 is specific for diphospho- and triphosphonucleosides. The Km values for ADP and ATP are 7.4 and 7.3 x 10(-4) M, respectively, and the purified enzyme has specific activities of 13 and 15.2 mumol of Pi/min/m of protein, respectively. It requires calcium or magnesium ions and it is insensitive to ATPase inhibitors, namely oligomycin, ouabain, and ruthenium red, and to levamisole, an inhibitor of alkaline phosphatase. Denaturation experiments, by heat and trypsin treatments, indicated that only one enzyme is involved. This is confirmed by the solubilization and purification process and by polyacrylamide gel electrophoresis. A 270-fold purification was obtained by centrifugation and successive column chromatography on Sepharose 4B and Affi-Gel blue. It is a glycoprotein with a molecular weight of 65,000 as estimated by polyacrylamide gel electrophoresis.