A new spectrophotometric assay for enzymes of purine metabolism. I. Determination of xanthine oxidase activity.

A new method for the determination of xanthine oxidase activity with xanthine or hypoxanthine is described. The hydrogen peroxide produced by the oxidation of the substrates is reduced by catalase in the presence of high concentrations of ethanol. The acetaldehyde formed is further oxidized by aldehyde dehydrogenase NAD or NADP-dependent. The reduction rate of the coenzymes were measured at 334 nm and utilized as indicators for the xanthine oxidase. The sensitivity of the method with xanthine as substrate can be doubled by the addition of uricase, which oxidizes uric acid to allantoin.