The chemistry of xanthine oxidase. 6. Variations in stability and the presence of an inhibitor in certain preparations

Abstract

The stabilities of 2 xanthine oxidase preparations have been compared under a variety of conditions; one of these preparations was found to be consistently more stable than the other. Kinetic experiments indicated that the more stable sample contained a xanthine oxidase inhibitor; the presence of this could account for the observed stability differences. Evidence bearing on the occurrence, formation and nature of the inhibitor are discussed briefly, and it is suggested that variations in its concentration may be responsible for certain discrepancies and anomalies in the properties of xanthine oxidase recorded in the literature.