An enzymatic spectrophotometric method for the determination of “oxypurines”(hypoxanthine plus xanthine) in urine and blood plasma

Abstract

A quantitative method for the determination of “oxypurines”(hypoxanthine plus xanthine) in the presence of relatively high concentrations of uric acid, as in urine and blood plasma, is described. The oxypurines are separated from the uric acid and, with plasma, from proteins, on a cation-exchange resin, eluted and oxidised enzymatically to uric acid by using xanthine oxidase (xanthine: oxygen oxidoreductase, E.C.1.2.3.2). The uric acid is then determined by the change in the value of E₂₉₂, which occurs when it is oxidised to allantoin by the highly specific enzyme uricase (urate: oxygen oxidoreductase, E.C.1.7.3.3). The accuracy and reproducibility of the method have been evaluated and a comparison with other methods is included in the discussion.