Action of Tyrosinase on Ortho-Substituted Phenols: Possible Influence on Browning and Melanogenesis

The action of tyrosinase on ortho-substituted monophenols (thymol, carvacrol, guaiacol, butylated hydroxyanisole, eugenol, and isoeugenol) was studied. These monophenols inhibit melanogenesis because they act as alternative substrates to L-tyrosine and L-Dopa in the monophenolase and diphenolase activities, respectively, despite the steric hindrance on the part of the substituent in ortho position with respect to the hydroxyl group. We kinetically characterize the action of tyrosinase on these substrates and assess its possible effect on browning and melanognesis. In general, these compounds are poor substrates of the enzyme, with high Michaelis constant values, K-m, and low catalytic constant values, k(cat), so that the catalytic efficiency k(cat)/K-m is low: thymol, 161 +/- 4 M-1 s(-1); carvacrol, 95 +/- 7 M-1 s(-1); guaiacol, 1160 +/- 101 M-1 s(-1).