牛血清蛋白在盐酸胍和尿素体系中变性的微量热研究

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

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△G和总吉布斯能△G(a),用变性中点的直线外推方法求出了表观变性焓△Hd.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△Hd在牛血清蛋白的pH=6.97和7.05时为350kJ·mol-1,在pH=9.30时为275kJ·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△Hd在牛血清蛋白的pH=6.97时为295kJ@mol-1,在pH=7.05和9.30时为230kJ·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.

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 △G and the total Gibbs energy △G（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 △Hd. 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 △Hd of BSA by guanidine chloride was 350 kJ·mmol^-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 △Hd 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.