Subcellular distribution of inorganic pyrophosphatase activity in various normal and neoplastic cell types.

Inorganic pyrophosphatase (PPiase) activity was measured in cell fractions of rat, mouse, and human erythrocytes; normal rat liver; Novikoff hepatoma; Morris 3924A hepatoma; and mouse Ehrlich and Sarcoma 37 ascites tumors. Despite high intracellular activities, when precautions were taken to maintain cell integrity, only negligible activities were found on the surface of intact erythrocytes, Novikoff ascites hepatoma, Ehrlich carcinoma, and Sarcoma 37 cells. Suspensions of intact Ehrlich and Sarcoma 37 cells exhibited low PPiase activity, but this was only about 1 to 2% of the intracellular activity and was completely accounted for by activity present in the suspension medium.

A microcolorimetric assay of inorganic pyrophosphatase.

A procedure is described for the assay of inorganic pyrophosphatase in tissues by a microcolorimetric procedure, taking advantage of the marked color intensification of phosphomolybdate by malachite green. Conditions are described for optimum enzyme activity, color stability, and sensitivity. With 1-cm cuvettes the AM660 is 100,000, allowing accurate measurement of Pi in the 1-nmol range.