A New Enzymatic Method for Assaying Serum Inorganic Pyrophosphatase

We developed a novel simple method to determine serum inorganic pyrophosphatase (PPase; EC 3.6.1.1) activity using purine nucleoside phosphorylase, xanthine oxidase and peroxidase, which method is applicable to automated analysis. Good reproducibility was demonstrated, with a coefficient of variation of 2.5 to 4.0% depending on the PPase activity. Good stability after color development was also observed. The presence of ascorbic acid, bilirubin, hemoglobin or intra-lipid did not influence the results. We also investigated the relationship between the activities of alkaline phosphatase (ALP; EC 3.1.3.1) and PPase. A strong positive correlation between ALP from bone and placenta and PPase was demonstrated with a correlation coefficient of 0.932 and 0.909, respectively. In contrast, ALP from liver showed a relatively weak correlation, with a correlation coefficient of 0.839. Further, placenta showed a higher ratio of PPase activity to ALP activity than did other tissues. PPase and ALP could not be distinguished by gel filtration or by ion-exchange chromatography.