McMinn J H, Sowa M J, Charnick S B, Paulaitis M E
Department of Chemical Engineering, University of Delaware, Newark 19716.
Biopolymers. 1993 Aug;33(8):1213-24. doi: 10.1002/bip.360330808.
Water sorption isotherms at 27 degrees C have been measured for lysozyme and chymotrypsin in suspensions of toluene, di(n-butyl) ether, n-propanol, and a solution of 1M n-propanol in benzene. Sorption isotherms for the different suspensions are compared by converting solvent water content to the thermodynamic activity of water in each solvent. The sorption behavior is also compared to that for the two proteins hydrated from the vapor phase. At low water activities, all sorption isotherms are similar when compared on the basis of water activity. However, at higher activities, water sorption by the proteins in the organic suspensions is suppressed relative to the sorption of water vapor. The greatest suppression is observed for n-propanol, which suggests that the suppression may be due to a competition for water-binding sites on the protein by the organic solvent. Sorption isotherms at low water activities have also been predicted using a thermodynamic model in which it is assumed that water binds selectively to the ionizable residues on the surface of the protein. A comparison of predicted and measured sorption isotherms shows that the model can provide reasonable estimates of water sorption in nonpolar or moderately polar organic solvent suspensions at low levels of hydration.
已测定了27摄氏度下溶菌酶和胰凝乳蛋白酶在甲苯、二正丁醚、正丙醇以及1M正丙醇的苯溶液悬浮液中的水吸附等温线。通过将溶剂中的水含量转换为每种溶剂中水的热力学活度，比较了不同悬浮液的吸附等温线。还将吸附行为与从气相水合的两种蛋白质的吸附行为进行了比较。在低水活度下，基于水活度比较时，所有吸附等温线都相似。然而，在较高活度下，相对于水蒸气的吸附，有机悬浮液中蛋白质对水的吸附受到抑制。在正丙醇中观察到的抑制作用最大，这表明这种抑制可能是由于有机溶剂与蛋白质上的水结合位点竞争所致。还使用了一个热力学模型预测了低水活度下的吸附等温线，该模型假设水选择性地结合到蛋白质表面的可电离残基上。预测的吸附等温线与实测吸附等温线的比较表明，该模型可以在低水合水平下合理估计非极性或中等极性有机溶剂悬浮液中的水吸附情况。
