Study of kinetics with respect to action of flavonoid from mulberry leaves on inhibition of activity of tyrosinase

采用超声波辅助法,以体积分数为60%的乙醇水溶液从新疆桑叶粉末中提取桑叶黄酮。以l-多巴为底物,采用酶动力学方法研究该提取物对酪氨酸酶的抑制作用。实验结果表明,桑叶黄酮提取物对酪氨酸酶有较强的抑制作用,其IC50为0.2 g·l-1。其对酪氨酸酶的抑制作用表现为可逆效应,抑制类型为混合型抑制,对游离酶的抑制常数(kI)和对酶-底物络合物的抑制常数(kIS)分别为366和873 Mg·l-1。dPPH实验显示新疆桑叶黄酮提取物具有一定的抗氧化作用,对dPPH自由基氧化作用相对活性的IC50为25 Mg·l-1,与VC效果相当。Flavonoid was extracted from powder of mulberry leaves planted in Xinjiang with 60%( vol) ethanol aqueous solution under assistance of ultrasonic wave.Adopting enzymatic kinetic method,inhibitory action of the extract on tyrosinase activity was studied using L- dopa as the substrate.Results showed that the flavonoid extract displays rather strong inhibitory action on activity of tyrosinase.Its IC50 was estimated as 0.2 g·L- 1.The inhibition mechanism was studied and it was found that the reaction is reversible and type of the inhibition belongs to the mixed type,with the inhibition equilibrium constants for inhibitor binding with free enzyme KI and with enzyme- substrate complex KISwere determined as 366 and 873 mg·L- 1respectively.The DPPH( 1,1-diphenyl-2-picrylhydrazyl) radical test results showed that the flavonoid extract has the antioxidant activity to a certain extent.The IC50 is 25 mg·L- 1that is similar to vitamin C.新疆维吾尔自治区高校科研计划科学研究重点资助项目(XJEDU2012I30); 新疆师范大学校级重点学科招标课题资助项目(XJMB-1

Inhibition of mushroom tyrosinase by flavonoid from Sorbus tianschanica Ruper in Xinjiang

以新疆天山花楸的茎为材料,采用超声波辅助法提取得到天山花楸黄酮类物质。以l-多巴为底物,运用酶动力学方法研究黄酮类物质对酪氨酸酶的抑制作用。结果表明:天山花楸黄酮类物质对酪氨酸酶有较强的抑制作用,导致酪氨酸酶二酚酶活力下降50%所需的提取物浓度(IC50)值为0.27 Mg/M l。对酪氨酸酶的抑制显示可逆的效应,抑制类型为混合型,对游离酶的抑制常数(kI)和酶-底物配位化合物的抑制常数(kIS)分别为0.218和0.313Mg/M l。1,1-二苯基-2-三硝基苯肼自由基(dPPH·)实验显示天山花楸黄酮类物质具有一定的抗氧化作用,引起dPPH·活性下降50%的黄酮类物质浓度(IC50)为0.18 Mg/M l。本研究为进一步开发利用天山花楸中的果蔬保鲜及美白成分提供了理论依据。Flavonoid was extracted from powder of Sorbus tianschanica Ruper stems under assistance of ultrasonic wave.Adopting enzymatic kinetic method,inhibitory action of flavonoid extract on the tyrosinase activity was studied using L-DOPA as substrate.Results showed that flavonoid extract from Sorbus tianschanica Ruper inhibited tyrosinase.Its IC50 was estimated as 0.27 mg / m L.The inhibition mechanism was studied and it was found that the reaction was reversible and type of the inhibition belonged to the mixed-type.The inhibition equilibrium constants for inhibitor binding with free enzyme KI and with enzyme-substrate complex KISwere determined as 0.218 and 0.313 mg / m L,respectively.The DPPH( 1,1-diphenyl-2-picrylhydrazyl) radical test results showed that flavonoid extract from Sorbus tianschanica Ruper had the antioxidant activity to a certain extent and the inhibitor concentration leading to 50% DPPH· free radical activity loss( IC50) was determined to be 0.18 mg /m L.The above study provides a basis for further development of the fruits and vegetables preservatives and whitening ingredient in the Sorbus tianschanica Ruper.国家自然科学基金(31260213); 新疆维吾尔自治区高校科研计划科学研究重点项目(XJEDU2012I30); 新疆维吾尔自治区教育厅重点实验室开放基金项目(XJSD2013-06