金属硫蛋白与Cd2+、Pb2+络合反应的微量量热滴定

金属硫蛋白（ｍｅｔａｌｌｏｔｈｉｏｎｅｉｎ,简称ＭＴ）是一类低分子量、富含半胱氨酸的金属结合蛋白,具有调节体内微量金属元素（Ｚｎ、Ｃｕ等）代谢、重金属解毒和清除自由基等多种生物学功能［１］．ＭＴ与金属离子的络合作用是发挥其功能的物质基础,哺乳动物ＭＴ每分子含２０个半胱氨酸巯基,可结合７个二价金属离子或１２个一价金属离子;通常,各种金属离子的结合能力与典型的硫酸盐型络合物的顺序一致,即 Ｚｎ（Ⅱ）＜ Ｐｂ（Ⅱ）＜ Ｃｄ（Ⅱ）＜ Ｃｕ（Ⅰ）, Ｈｇ（Ⅰ）, Ｈｇ（Ⅱ）, Ｂｉ（Ⅲ）［２］．哺乳动物Ｃｄ７－…     

金属硫蛋白与Cd2+、Pb2+络合反应的微量量热滴定

Metallothionein, a class of low molecular weight, metal- and cysteine-rich Proteins, are postulated to play a central role in metal-related biological processes such as the detoxification of Cd2+and Pb2+. The thermal Properties of the interactions of rabbit liver Zn_7MT2 and apo-MT2 with Cd2+ and Pb2+ were studied using isothermal titration calorimeter. The same product Cd_7MT formed in the reactions of Cd2+ with Zn_7MT2 and apo-MT2, while the reactions of Ph2+ with Zn_7MT2 and apo-MT2 Produced two MT species Ph_7MT and Ph_7MT'. The thermodynamic parameters (△H、 △G、 △S, etc. ) for the reactions of MT with 1 mol metal ions were measured at 293.15 K, pH 4.70. All of these reactions are spontaneous, exothermic processes. The values of △G and K show that Cd2+ is more affinitive to MT than Ph2+. The equilibrium constants K of the replacement reactions of Zn_7MT2 by 1 mol Cd2+ and Pb2+ are 2. 7×105 and 1. 3×105 respectively, that means the concentrations of free Cd2+ and Pb2+ are depressed to about 1. 0×10-5 after the reactions with Zn_7MT2. These data can be used to evaluate quantitatively the ability of MT in Cd2+ and Pb2+ detoxificatio.