肉桂腈抑制酪氨酸酶活性的动力学研究

Inhibitory kinetics of cinnamonitrile on tyrosinase activity

在30℃、pH6.8的Na2HPO4-NaH2PO4缓冲体系中,采用酶动力学方法研究了肉桂腈对酪氨酸酶单酚酶和二酚酶活力的抑制动力学。实验结果表明,肉桂腈对酪氨酸酶单酚酶和二酚酶活性均有良好抑制作用,对单酚酶和二酚酶活力的相对抑制率达到50%的肉桂腈浓度(IC50)分别为0.13mmol/L和0.62mmol/L。肉桂腈能延长单酚酶的迟滞时间,0.2mmol/L肉桂腈能使迟滞时间由2min延长至2.7min。Lineweaver-Burk图显示肉桂腈对二酚酶的抑制作用表现为非竞争性可逆抑制,表观米氏常数(Km)为0.90mmol/L,抑制常数(KI)为0.64mmol/L。

The inhibitory kinetics of cinnamonitrile on the activity of monophenolase and diphenolase contained in tyrosinase was studied by enzymological kinetic method with Na2HPO4-NaH2PO4 buffer solution（pH6.8） at 30 ℃. Cinnamonitrile was found to inhibit the monophenolase and diphenolase activity of tyrosinase well. The cinnamonitrile concentrations leading to 50% inhibitory rate（IC50） were 0.13 mmol/L for monophenolase and 0.62 mmol/L for diphenolase. Cinnamonitrile can extend the lag time of tyrosinase for oxidation of L-tyrosine, 0.2 mmol/L of cinnamonitrile resulted in the extension of lag time from 2 min to 2.7 min. The inhibition kinetics of cinnamonitrile analyzed by Lineweaver-Burk plots demonstrated a noncompetitive inhibitor for the oxidation of L-DOPA, the apparent Michaelis comstant, Km, and the inhibition constant for inhibitor binding with enzyme, KI, were determined to be 0.90 mmol/L and 0.64 mmol/L respectively.