Abstract: The water extract from the flowers of peony was prepared.Scavenging effect on hydroxyl free radicals,which were generated from the Fenton reaction of the water extracts was detected by spectrophotometry.The inhibitory action of water extracts from peony on the activity of monophenolase and diphenolase contained in tyrosinase were studied by using L-tyrosine and L-DOPA (L-3,4-dihydroxyphenylalanine) as substrate separately at 30 ℃ with Na₂HPO₄-NaH₂PO₄ as buffer solution (pH=6.8).The results showed that the water extracts from peony can scavenge hydroxyl free radicals effectively.The free radical elimination ratio of the water extracts achieves 91.67% when the mass concentration of the peony water extract is 1.00 g·L^-1.The water extract from peony displays good inhibitory effect to both monophenolase and diphenolase activity of tyrosinase with IC₅₀ at 0.015 g·L^-1 for monophenolase and 0.210 g·L^-1 for diphenolase.The inhibition kinetics of the water extracts analyzed by Lineweaver-Burk plots demonstrated a non-competitive inhibitor for diphenolase and the Michaelis constant (K_m) was determined to be 0.4 mmol·L^-1.

Key words: water extracts from peony, hydroxyl free radicals, tyrosinase