竹笋壳黄酮提取物对酪氨酸酶活性影响的动力学研究

酪氨酸酶是合成黑色素细胞的关键酶,为了探讨竹笋壳黄酮提取物对酪氨酸酶活性的影响,对竹笋壳中的黄酮类物质进行提取纯化,并采用酶动力学方法研究了笋壳黄酮提取物对酪氨酸酶单酚酶和二酚酶的抑制作用。结果表明:笋壳黄酮提取物导致单酚酶和二酚酶活力下降50%的抑制剂浓度(IC50)分别为5.6和4.6mg/mL;笋壳黄酮提取物对酪氨酸酶单酚酶的迟滞时间有明显的延长效应,8.0mg/mL的笋壳黄酮提取物可使单酚酶的迟滞时间从1.4min延长到4.2min;笋壳黄酮提取物对酪氨酸酶二酚酶的抑制作用表现为混合型可逆抑制,笋壳黄酮提取物对游离酶的抑制常数(Ki)为3.1mmol/L,对酶底物络合物的抑制常数(Kis)为5.7mmol/L;笋壳黄酮提取物对酪氨酸酶单酚酶和二酚酶均有抑制作用。

Kinetics study on the effect of bamboo shell flavonoid extract on tyrosinase activity

Tyrosinase is key enzyme for the biosynthesis of melanocyte. In order to explore the effects of flavonoid on the activity of tyrosinase, we extracted flavonoid from bamboo shells by ethanol ultrasonication and purified it by AB-8 macroporous resin. The inhibitory effects of bamboo shell flavonoid extract on the monophenolase and diphenolase activities of tyrosinase were studied by an enzyme kinetic method. The concentration of bamboo shell flavonoid extract which caused the enzymatic activity loss of 50% was 5.6 mg/mL for monophenolase and 4.6 mg/mL for diphenolase. Bamboo shell flavonoid extract of 8.0 mg/mL extended the time of delay in monophenolase from 1.4 to 4.2 min. An analysis of inhibition kinetics suggested that bamboo shell flavonoid extract was a reversible mixed inhibitor for the oxidation of L-DOPA, and the inhibition equilibrium constants for inhibitor binding with free enzyme Ki and with enzyme-substrate complex Kis were 3.1 mmol/L and 5.7 mmol/L, respectively. The results indicate that the bamboo shell flavonoid extract can inhibit the monophenolase and diphenolase activities of tyrosinase.