Relative metabolism of quinones to semiquinone radicals in xanthine oxidase system

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Abstract
Rates of enzymatic single‐electron reduction of some myotoxc quinones to semiquinone metabolites in an in vitro xanthine oxidase/hypoxanthine/catalase system varied widely. Naphthoquinones, especially juglone, were found to undergo rapid single‐electron reduction. Benzoquinones and benzoquinoneimines, as well as phenanthrene‐9,10‐quinone, benzo[a]pyrene‐3,6‐quinone, and diethylstilbestrolquinone, were also actively reduced. The anthraquinones danthron, doxorubicin and emodin were poorly metabolized in this system. N‐Acetylcysteine inhibited quinone‐stimulated cytochrome C reduction at high concentrations. The results of this study are discussed with respect to cytotoxicity and mutagenicity of selected quinones.