Abstract: Objective To evaluate the effects of monomers of aloin, cinnamic acid and sophocarpidine on the acitivity of tyrosinase,so as to provide depigmenting agents in the treatment of hyperpigmentation disorders and cosmetics additives as well. Methods Tyrosinase activity was estimated by measuring the oxidation rate of DL dopa. The inhibitory pattern of each monomers was determined according to their Lineweaver Burk curve as compared to controls. Results Aloin,cinnamic acid and sophocarpidine down regulated the activity of tyrosinase. The inhibitory rates were significantly higher in cinnamic acid group(2 mmol/L, 0.5 mmol/L), aloin group (2 mmol/L)and sophocarpidine group than those in hydroquinone group (0.5 mmol/L)(P<0.05). Conclusion Tyrosinase activity can be greatly inhibited by cinnamic acid, aloin and sophocarpidine, of which sophocarpidine functions as an uncompetitive inhibitor, while aloin and cinnamic acid as mixed type inhibitors of tyrosinase.

Key words: Monophenol monooxygenase, Cinnamic acid, Aloin, Sophocarpidine