Protein thermal stability was analyzed by a solution thermodynamic approach. The small energetic differences in hydrogen-bonds (HB) among amino acid resdues and water molecules were proved to be amplified by the large number of HB involved to bring about the equilibrium shift from folding to unfolding of proteins. In aqueous solutions, water activity (Aw) plays a key role in protein stability. Therefore, Aw was precisely determined for various solutions and its relationship with solution structure was discussed. Wyman-Tanford analysis based on Aw showed linear regressions, without exception, between protein unfolding-ratio and Aw for lysozyme, ribonuclease A, and α-chymotrypsinogen A in various solutions with sugars, osmolytes, alcohols, and protein denaturant. From this linear regression, the free energy difference, ΔΔG, for a protein in a solution and in pure water, was easily obtained. Protein stability in a solution was proved to be determined by a balance between hydration and solute-binding effects to the protein and also by solution structure, which indirectly affects the hydrophobic interaction in a protein molecule. Temperature dependence of HB on protein stability suggested its interrelationship with hydrophobic interaction.

中文翻译：

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溶液热力学方法，用于分析水溶液中的蛋白质稳定性。

通过溶液热力学方法分析蛋白质的热稳定性。氨基酸残基和水分子之间氢键（HB）的小能量差异已被大量HB放大，从而引起蛋白质从折叠到展开的平衡转变而被放大。在水溶液中，水活度（Aw）在蛋白质稳定性中起关键作用。因此，可以精确地确定各种溶液的Aw，并讨论其与溶液结构的关系。基于Aw的Wyman-Tanford分析显示，在糖，渗透液，酒精和蛋白质变性剂的各种溶液中，溶菌酶，核糖核酸酶A和α-胰凝乳蛋白酶原A的蛋白质展开率与Aw之间无一例外地线性回归。根据这种线性回归，自由能差ΔΔG 容易获得溶液中和纯水中的蛋白质。事实证明，溶液中的蛋白质稳定性取决于水合和溶质对蛋白质的结合效果之间的平衡，也取决于溶液结构，溶液结构间接影响蛋白质分子中的疏水相互作用。HB对蛋白质稳定性的温度依赖性表明其与疏水相互作用的相互关系。