A new enzymatic method for the determination of inorganic phosphate and its application to the nucleoside diphosphatase assay

A new enzymatic method has been developed for the determination of inorganic phosphate, in which purine nucleoside phosphorylase and xanthine oxidase are used as indicator enzymes. This method has been applied to the assay of nucleoside diphosphatase. Incidental to this work, the apparent Michaelis constant of phosphate for calf spleen purine nucleoside phosphorylase was determined to be 0.25 mm, and the extinction coefficient of uric acid at 293 nm and pH 7.4 was found to be 13.0 × 10³m^?1 cm^?1.