INHIBITORY EFFECTS OF ALPHA-VINIFERIN AND RESVERATROL ON THE L-DOPA OXIDASE ACTIVITY OF TYROSINASE

Tyrosinase catalyses the rate-limiting step in the biosynthesis of mel anin, a determinant of skin colour which is involved in local human hy perpigmentation diseases. We have analysed the effects of alpha-vinife rin and resveratrol on the L-dopa oxidase activity of tyrosinase. Both alpha-viniferin and resveratrol had dose-dependent inhibitory effects on the enzyme activity, showing 50% of inhibition as compared with th e control at concentrations of 7.3 x 10(-5) M and 7.2 x 10(-5) M respe ctively. According to a kinetic study of tyrosinase with L-dopa as a s ubstrate, alpha-viniferin had a K-EI value of 1.0 x 10(-4) to 1.1 x 10 (-4) M and a K-EIS value of 5.8 x 10(-5) to 5.9 x 10(-5) M, and resver atrol a K-EI value of 6.9 x 10(-5) to 7.4 x 10(-5) M and a K-EIS value of 4.6 x 10(-5) to 5.0 x 10(-5) M. Therefore, alpha-viniferin and res veratrol were similar in their inhibitory potency on the L-dopa oxidas e activity of tyrosinase. Both were identified as mixed-type inhibitor s, exhibiting a K-EI value larger than the K-EIS value on the enzyme a ctivity with L-dopa as a substrate. (C) 1998 Lippincott-Raven Publishe rs.