Property of the antioxidant activity using xanthine oxidase reaction

Abstract

Inhibitory activity of the superoxide anion (O2−) generation catalyzed by xanthine oxidase (EC 1.1.3.22) with natural products was used to estimate the antioxidant activity. To understand properties about the activity, we examined antioxidant activity of anacardic acids, alkyl gallates and flavonoids. Xanthine oxidase consisted of several oxid‐reduction forms in the molecule. The oxidized forms catalyzed O2− generation from oxygen but the reduced forms catalyzed only hydrogen peroxide formation. We deduced that antioxidants affected three reactions, (A), (B) and (C) to indicate antioxidant activity. In reaction (A), antioxidants function inhibitors of xanthine oxidase reaction, and both uric acid formation and O2− generation were suppresses. In the reaction (B), antioxidants function as reducing reagents of xanthine oxidase, and the reduced enzyme cannot generate O2−. In the reaction(C), antioxidants function as scavengers of O2− generated by xanthine oxidase. We also indicate that effects of antioxidants on reaction (A) and (B) are stronger than those on reaction (C).