EFFECT OF BENZOIC-ACID AND SOME OF ITS DERIVATIVES ON THE RATE OF DL-DOPA OXIDATION BY MUSHROOM TYROSINASE

Vanillic acid and salicylic acid inhibited the rate of dihydroxyphenyl alanine (DL-DOPA) oxidation to dopachrome (lambda(max) = 475 nm) by ty rosinase at all concentrations tested. Benzoic acid and p-hydroxybenzo ic acid (PHBA), at relatively low concentrations, slightly stimulated the rate of DL-DOPA oxidation, whereas at higher concentrations each i nhibited the reaction. p-Hydroxybenzoic acid methyl ester (PHBAME), at relatively low concentrations, had a pronounced synergistic effect on the reaction, whereas at relatively high concentrations it inhibited the rate of DL-DOPA oxidation. The synergistic effect of 1.6-6.6 mM PH BAME on the rate of DL-DOPA oxidation to dopachrome was found to be on ly art apparent effect due to the ability of PHBAME to be hydroxylated very slowly by tyrosinase to a yellow pigmented product(s) with DL-DO PA sewing as a reductant (AH(2)) for the hydroxylation reaction, thus hastening the conversion of PHBAME to pigmented product(s). Vanillic a cid, salicylic acid, benzoic acid and PHBA could not be hydroxylated b y tyrosinase.