总银杏酸对酪氨酸酶活性的影响及动力学研究

Kinetics and Effect of Total Ginkgolic Acids on Tyrosinase Activity

研究了总银杏酸(C13∶0,C15∶1,C17∶2,C15∶0,C17∶1)对酪氨酸酶单酚、二酚酶活力的影响及其抑制动力学。在28℃,p H=6.8的Na2HPO4-Na H2PO4缓冲体系中,测试总银杏酸对酪氨酸酶催化反应进程的影响、酶活性抑制率以及抑制动力学参数。实验表明,总银杏酸对酪氨酸酶单酚酶和二酚酶活性均有抑制作用,单酚酶和二酚酶活力下降50%的总银杏酸质量浓度(IC50)分别为0.03 g/L和0.20 g/L。总银杏酸能延长单酚酶反应的迟滞时间,对二酚酶的抑制作用表现为可逆效应。Lineweaver-Burk图显示总银杏酸对二酚酶的抑制作用表现为竞争性抑制,抑制常数KI=75.20 mg/L。

The kinetics of inhibitory effect of total ginkgolic acids（C13∶0,C15∶1,C17∶2,C15∶0,C17∶1）on the monophenolase and diphenolase activity of mushroom tyrosinase was studied.The effect on catalytic reaction of tyrosinase process,the enzyme activity inhibition rate and inhibitory kinetic parameters of total ginkgolic acids were tested in the Na2HPO4-Na H2PO4 buffer system kept at 28 ℃and p H = 6.8.It was found that the total ginkgolicacids efficiently inhibits both monophenolase and diphenolase activities of mushroom tyrosinase under experiment conditions.The concentrations of the total ginkgolic acids leading to 50% rate inhibition（IC50） on monophenolase and diphenolase activity were calculated to be 0.03 g/L and 0.20 g/L respectively.The presence of the total ginkgolic acids also prolongs the lag period in the oxidation process of L-tyrosine via tyrosinase.A reversible inhibition of diphenolase by the total ginkgolic acids has been found,indicating that the inhibitor binds the enzyme reversibly rather than reacts with it destructively.The Lineweaver-Burk plot demonstrates a competitive behavior of the total ginkgolic acids in the tyrosinase oxidation of L-DOPA,with theinhibition constant KIbeing at 75.20 mg/L.