Enzyme-catalyzed Free Radical Reactions with Nicotinamide Adenine Nucleotides

The superoxide radical produced by xanthine oxidase can be coupled to oxidation of NADH in the presence of lactate dehydrogenase. The oxidized product has been identified as the enzymatically active NAD⁺. If the superoxide radical is determined quantitatively by its interaction with ferricytochrome c under similar conditions, it can be estimated that for each superoxide radical produced in the xanthine oxidase system an average of 6.2 molecules of NADH can be oxidized, which indicates a chain reaction in the oxidation process. The lactate dehydrogenase-catalyzed oxidation activity can be inhibited by either superoxide dismutase or oxamate.