The accumulation of l-3:4-dihydroxyphenylalanine in the tyrosinase-tyrosine reaction

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Abstract
Dopa would not be expected to accumulate in the tyrosinase-tyrosine reaction because it is more rapidly attacked by the enzyme than is tyrosine. Possible reasons for this are discussed and it is shown to be due to the reducing action of 5:6-dihydroxydihydroin-dole-[alpha]-carboxylic acid on dopa quinone. These are presumed to interact with the formation of 5:6-dihydroxy-indole-[alpha]-carboxylic acid (hallachrome) and dopa, respectively. Addition of the dihydroindole derivative to the tyrosinase-tyrosine system results in an increased production of dopa. Addition of ascorbic acid to the tyrosinase-tyrosine system also increases the production of dopa, presumably by reduction of dopa quinone. Hallachrome can act as a H acceptor in the succinoxidase-succinate system and xanthineoxidase-xanthine system, but conclusive evidence of increased dopa accumulation was not obtained. Potato and mealworm tyrosinase were used.