Abstract: The active effects of caffeic acid on the activity of monophenolase and diphenolase contained in mushroom tyrosinase was studied by enzymological kinetic method at 30℃, and pH 6.8 with Na2HPO4-NaH2PO4 as buffer solution. Caffeic acid was found capable to activate both the monophenolase and diphenolase activities of tyrosinase. The caffeic acid concentration leading to 50% activtion rate (IC50) is 0.61 mmol/L for monophenolase activity or 1.49 mmol/L for diphenolase activity. Caffeic acid can remove the lag time of tyrosinase for oxidation of L-tyrosine. The activation kinetics analyzed by Lineweaver-Burk plots of caffeic acids was shown to be of mixed activator characteristics for the oxidation of L-DOPA. The Michaelis constants, Km, become 0.31, 0.25, 0.20, 0.15 mmol/L respectively when the caffeic acids are 0, 0.50, 1.0, 1.50mmol/L.

Key words: tyrosinase, caffeic acid, inhibitory effect, kinetics, monophenolase, diphenolase