DETERMINATION OF HUMAN PLASMA XANTHINE-OXIDASE ACTIVITY BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

An assay for human plasma xanthine oxidase activity was developed with pterin as the substrate and the separation of product (isoxanthopteri n) by high-performance liquid chromatography with a fluorescence detec tor. The reaction mixture consists of 60 mu l of plasma and 240 mu l o f 0.2 M Tris-HCl buffer (pH 9.0) containing 113 mu M pterin. With this assay, the activity of plasma xanthine oxidase could be easily determ ined despite its low activity. As a result, it could be demonstrated t hat the intravenous administration of heparin or the oral administrati on of ethanol did not increase plasma xanthine oxidase activity in nor mal subjects, and also that plasma xanthine oxidase activity was highe r in patients with hepatitis C virus infection than in healthy subject s or patients with gout. In addition, a single patient with von Gierke 's disease showed a marked increase in the plasma activity of this enz yme, relative to that apparent in normal subjects.