牛血清蛋白在盐酸胍和尿素体系中变性的微量热研究

在30 ℃时用恒温微量热法研究了不同pH值下盐酸胍、尿素诱导牛血清蛋白变性的过程. 并用Privalov提出的简单键合模型对量热数据进行了分析, 计算了表观键合常数K, 简单键合的单个表观键合自由能ΔG和总吉布斯能ΔG(a), 用变性中点的直线外推方法求出了表观变性焓ΔH_d. 实验结果表明, 牛血清蛋白与盐酸胍的键合在碱性条件下更易进行, 牛血清蛋白在盐酸胍溶液中的变性焓ΔH_d在牛血清蛋白的pH＝6.97和7.05时为350 kJ?mol^－1, 在pH＝9.30时为275 kJ?mol^－1, 表明牛血清蛋白在接近中性时较稳定. 而牛血清蛋白与尿素的键合在酸性条件下更易进行, 此变性焓ΔH_d在牛血清蛋白的pH＝6.97时为295 kJ?mol^－1, 在pH＝7.05和9.30时为230 kJ?mol^－1. 此结果说明牛血清蛋白在两种变性剂溶液中的展开程度是不同的.

Denaturation Study of Bovine Serum Albumin Induced by the Guanidine Chloride or Urea by Microcalorimetry

The denaturation of bovine serum albumin (BSA) induced by guanidine chloride or urea at different pH values was studied by isothermal microcalorimetry measurements at 30 ℃. The simple bonding model, which was developed by Privalov, was employed to obtain the apparent bonding constant K, the apparent singular bonding Gibbs bonding energy ΔG and the total Gibbs energy ΔG(a) between the protein and denaturant from analyzing the calorimetric data. Furthermore, the linear extrapolation at the midpoint of transition was employed to determine the apparent denaturation enthalpy ΔH_d. The results showed that, for guanidine chloride, the bonding between BSA and guanidine chloride could proceed more easily in an alkaline condition, and the apparent denaturation enthalpy ΔH_d of BSA by guanidine chloride was 350 kJ?mol^－1 at pH 6.97 and 7.05, while it was 275 kJ?mol^－1 at pH 9.30, which indicated that BSA was more stabilized in a neutral condition. But for urea, the bonding between BSA and urea would proceed more easily in an acidic condition, and the apparent denaturation enthalpy ΔH_d of BSA by urea was 295 kJ?mol^－1 at pH 6.97, while 230 kJ?mol^－1 at pH 7.05 and 9.30. The results indicated that the expanding degree of BSA in the two denaturants was different.