Metabolism of 1-naphthol by tyrosinase

1-Naphthol was metabolized by the polyphenol oxidase, tyrosinase, primarily to 1,2-naphthoquinone and to small amounts of 1,4-naphthoquinone as well as to covalently bound products. The inhibition of covalent binding by ethylenediamine, which reacts specifically with 1,2-naphthoquinone but not 1,4-naphthoquinone, suggested that most of the covalent binding was due to 1,2-naphthoquinone or a metabolite of similar structure. The activation by tyrosinase of 1-naphthol to covalently bound products suggested that it may alter the reaction kinetics of the enzyme. This was investigated by studying the effects of 1-naphthol on the tyrosinase-catalysed oxidation of 4-hydroxyanisole. Preincubation of tyrosinase with 1-naphthol increased the lag period of the oxidation of 4-hydroxyanisole, which may be due to a decrease in the amount of active enzyme, as well as to a reaction of 1-naphthol with 3,4-anisylquinone, an oxidation product of 4-hydroxyanisole. The metabolic activation of 1-naphthol by tyrosinase to covalently bound species suggests that 1-naphthol or a structurally related derivative may be of potential therapeutic application in the treatment of cells high in tyrosinase activity, such as certain melanomas.