Abstract— An investigation into the mechanism of lipid peroxidation catalyzed by xanthine oxidase showed a dependence upon superoxide, singlet oxygen and adenosine 5'‐diphosphate chelated iron (ADP‐Fe3+). In the absence of ADP‐Fe3+ or in the presence of superoxide dismutase there is complete inhibition of enzymatic peroxidation. Initiation of peroxidation likely occurs through an ADP‐perferryl ion complex formed by ADP‐Fe3+ and superoxide. Use of the singlet oxygen trapping agent 2,5‐diphenylfuran showed that singlet oxygen does not participate in the initiation of peroxidation but rather in the propagation of peroxidation. The mechanisms of NADPH‐cytochrome P450 reductase‐catalyzed and ADP‐Fe2+ catalyzed lipid peroxidation parallel that of xanthine oxidase in that initiation occurs through a superoxide dismutase‐sensitive reaction and that singlet oxygen is present during propagation of lipid peroxidation.

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