Tanaka A, Flanagan J, Sturtevant J M
Department of Chemistry, Yale University, New Haven, Connecticut 06511.
Protein Sci. 1993 Apr;2(4):567-76. doi: 10.1002/pro.5560020408.
The effects of eight mutations on the thermodynamics of the reversible thermal unfolding of staphylococcal nuclease have been determined over a range of pH and protein concentration by means of differential scanning calorimetry. Variation of the protein concentration was included in our study because we found a significant dependence of the thermodynamics of protein unfolding on concentration. Values for the change in the standard free energy of unfolding, delta delta G0d, produced by the mutations in the pH range 5.0-7.0 varied from 1.9 kcal mol-1 (apparent stabilization) for H124L to -2.8 kcal mol-1 (apparent destabilization) for L25A. As has been observed in numerous other cases, there is no correlation in magnitude or sign between delta delta G0d and the corresponding values for delta delta Hd and T delta delta S0d, the latter quantities being in most cases much larger in magnitude than delta delta G0d. This fact emphasizes the difficulty in attempting to correlate the thermodynamic changes with structural changes observed by X-ray crystallography.
通过差示扫描量热法，在一系列pH值和蛋白质浓度范围内，测定了8种突变对葡萄球菌核酸酶可逆热解折叠热力学的影响。我们的研究纳入了蛋白质浓度的变化，因为我们发现蛋白质解折叠的热力学对浓度有显著依赖性。在pH值5.0 - 7.0范围内，突变产生的解折叠标准自由能变化值ΔΔG0d，从H124L的1.9千卡/摩尔（明显稳定）到L25A的 - 2.8千卡/摩尔（明显不稳定）不等。正如在许多其他情况下所观察到的，ΔΔG0d与相应的ΔΔHd和TΔΔS0d值在大小或符号上均无相关性，后两个量在大多数情况下绝对值比ΔΔG0d大得多。这一事实凸显了试图将热力学变化与X射线晶体学观察到的结构变化相关联的困难。
