THE EFFECT OF TRYPTOPHAN ON DOPA-OXIDATION BY MELANOSOMAL TYROSINASE

1. Tryptophan has been shown to inhibit dopa-oxidation by melanosomal tyrosinase. 2. The inhibition is of mixed-type with K(i) = 1.6 x 10(-3 ) m. 3. Tryptophan does not interact with the oxidation product of the dopa-oxidase reaction. 4. Neither oxygen nor hydroxyl radicals are in volved in the inhibition found in presence of tryptophan. 5. Tryptopha n, like dopa, also inhibits tyrosine hydroxylase and dopa-oxidase acti vity of melanosomal tyrosinase and its inhibitory mechanism differs fr om inhibition due to non-substrate type compounds like cysteine, ascor bic acid. 6. These experiments together with previous findings suggest that the status of tryptophan may be similar to that of dopa in relat ion to regulation of melanogenesis.