An amperometric-enzymatic method for assays of inorganic phosphate and adenosine deaminase in serum based on the measurement of uric acid with a dialysis membrane-covered carbon electrode

The concentration of inorganic phosphate (Pi) and activity of adenosine deaminase (ADA) in human serum were determined by measuring the anodic current of uric acid with a dialysis membrane-covered carbon electrode in the presence of purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) in a test solution. Uric acid was produced by the enzyme-catalyzed reactions in the solution containing serum, and the uric acid concentration was proportional to the concentration of Pi or the activity of ADA in the serum containing solution under appropriate conditions. The present method is free from the interference from proteins and oxidizable substances existing in serum samples. The Pi concentrations and ADA activities of twenty human serum samples determined by the present method were in excellent agreement with those determined by the conventional colorimetric-enzymatic methods, correlation coefficients between the two sets of results being 0.986 and 0.995, respectively. Advantages of the present method are discussed in comparison with the method using an electrode with immobilized PNP and XOD.