咖啡酸激活酪氨酸酶催化反应的动力学研究

Kinetics of Tyrosinase Catalyzing Reaction Activated by Caffeic Acid

在30℃,pH6.8的Na2HPO4-NaH2PO4缓冲体系中,采用酶动力学方法研究了咖啡酸对酪氨酸酶单酚酶和二酚酶活力的激活效应。实验结果表明,咖啡酸对酪氨酸酶单酚酶和二酚酶活性均有激活作用,对单酚酶和二酚酶活力的相对激活率达到50%的咖啡酸浓度(IC50)分别为0.27mmol/L和1.35mmol/L。咖啡酸能消除单酚酶催化反应的迟滞时间,对二酚酶的激活作用表现为混合性激活,当咖啡酸浓度为0、0.50、1.0、1.50mmol/L时,米氏常数Km分别为0.31、0.25、0.20、0.15mmol/L。

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% aetivtion 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.