Major Primary Cytotoxic Product of 4‐Hydroxyanisole Oxidation by Mushroom Tyrosinase Is 4‐Methoxy Ortho Benzoquinone

It has been shown previously that the initial product of mushroom tyrosinase-catalysed oxidation of the monophenol 4-hydroxyanisole (4HA) is 4-methoxy ortho benzoquinone (4-MOB). This study presents evidence that 4-MOB is primarily responsible for the cytotoxicity of 4HA oxidation products in vitro. Equivalent toxicity in a model system was produced by products of tyrosinase catalysed oxidation of 4HA and by synthetic 4-MOB. Cytotoxicity was estimated both by a blebbing assay and by plating efficiency of exposed cells. HPLC analysis of the reaction mixture revealed a positive correlation between cytotoxicity and 4-MOB concentration.