鞣酸对蘑菇酪氨酸酶的抑制作用

The Inhibitory Effect on Mushroom Tyrosinase by Tannic Acid

酪氨酸酶是一种同时具有单酚酶和二酚酶活力的氧化酶.研究鞣酸对蘑菇酪氨酸酶活力的影响,结果表明鞣酸对蘑菇酪氨酸酶的单酚酶和二酚酶活性都有抑制作用.鞣酸对单酚酶活力的影响主要表现于它能显著延长酶作用的迟滞时间,而对稳态活力的影响不大.2.0μmol/L鞣酸可以使单酚酶的迟滞时间从104.7 s延长到333.6 s,增大2倍以上,而酶的稳态活力仅下降19.8%.鞣酸对二酚酶的抑制作用显示浓度效应,测定导致酶活力下降50%的抑制剂浓度(IC50)为65μmol/L.鞣酸对二酚酶的效应为可逆的竞争性的抑制,抑制常数KI为36.3μmol/L.

Tyrosinase （1.14.18.1） is an enzyme that has both monophenolase activity and diphenolase activity. In this paper,tannic acid was discovered tO inhibit both the monophenolase activity and the o-diphenolase activity. The major effect of tannic acid on monophenolase activity is on the lag time of the enzyme for oxidation of L-tyrosine, which was lengthened obviously while the steadystate rate of monophenolase decreased slightly with the increase of concentration of tannic acid. 2 μmol/L of tannic acid resulted in the lag time extension from 104. 7 s to 333. 6 s,and only 19.8% lost of the steady-state rate of monophenolase could be observed. The inhibition kinetics and mechanism of tannic acid on the diphenolase activity of the enzyme has been studied. The results show that the inhibition of tannic acid is a reversible reaction with remaining enzyme activity. The IC50 ,inhibitor＇s concentration leading to 50 % activity lost,is estimated to be 65 μmol/L. The inhibition kinetics analyzed by Lineweaver-burk plots shows that tannic acid is a competitive inhibitor for the oxidation of L-DOPA,and its inhibition constant is 36.3μmol/L.