Metabolism of polycyclic compounds. 13. Enzymic hydroxylation of naphthalene by rat-liver microsomes

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Abstract
The oxidation of naphthalene to 1-naphthol and l,2-dihydro-l,2-dihydroxynaphthalene by rat-liver microsomes in the presence of reduced triphosphopyridine nucleotide and oxygen appears to involve 2 different enzyme systems. The system does not form 2-naphthol. In pyrophosphate buffer, pH 7.4, the rate of formation of 1-naphthol is doubled by 5 mM caffeine, and the rate of formation of l,2-dihydro-l,2-dihydroxynaphthalene is not altered. At pH 8.1 the rate of formation of l,2-dihydro-l,2-dihydroxynaphthalene is also increased. In 2-amino-2-hydroxymethylpropane-l,3-diol buffer, pH 8.2, the rate of formation of both metabolites falls off after 15 minutes but the initial rate of formation of 1,2-dihydro-i,2-dihydroxynaphthalene only is maintained if 2.5 mM -cysteine is present. The formation of both metabolites is inhibited by methylene blue, flavine mononucleotide and mercaptide-forming compounds but not by metal-binding compounds.