Carra J H, Anderson E A, Privalov P L
Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218.
Protein Sci. 1994 Jun;3(6):944-51. doi: 10.1002/pro.5560030609.
Using high-sensitivity differential scanning calorimetry, we reexamined the thermodynamics of denaturation of staphylococcal nuclease. The denaturational changes in enthalpy and heat capacity were found to be functions of both temperature and pH. The denatured state of staphylococcal nuclease at pH 8.0 and high temperature has a heat capacity consistent with a fully unfolded protein completely exposed to solvent. At lower pH values, however, the heat capacity of the denatured state is lower, resulting in a lower delta Cp and delta H for the denaturation reaction. The acid-denatured protein can thus be distinguished from a completely unfolded protein by a defined difference in enthalpy and heat capacity. Comparison of circular dichroism spectra suggests that the low heat capacity of the acid-denatured protein does not result from residual helical secondary structure. The enthalpy and heat capacity changes of denaturation of a less stable mutant nuclease support the observed dependence of delta H on pH.
我们使用高灵敏度差示扫描量热法重新研究了葡萄球菌核酸酶的变性热力学。发现焓和热容的变性变化是温度和pH值的函数。在pH 8.0和高温下，葡萄球菌核酸酶的变性状态具有与完全暴露于溶剂中的完全展开的蛋白质一致的热容。然而，在较低的pH值下，变性状态的热容较低，导致变性反应的ΔCp和ΔH较低。因此，酸变性蛋白可以通过焓和热容的特定差异与完全展开的蛋白区分开来。圆二色光谱的比较表明，酸变性蛋白的低热容不是由残留的螺旋二级结构引起的。一种稳定性较低的突变核酸酶变性的焓和热容变化支持了观察到的ΔH对pH的依赖性。
