Liu Wei, Bratko Dusan, Prausnitz John M, Blanch Harvey W
Chemical Engineering Department, University of California, Berkeley, CA 94720, USA.
Biophys Chem. 2004 Feb 15;107(3):289-98. doi: 10.1016/j.bpc.2003.09.012.
Alcohols have been widely used as protein denaturants, precipitants and crystallization reagents. We have studied the effect of alcohols on aqueous hen-egg lysozyme self-interactions by measuring the osmotic second virial coefficient (B22) using static light scattering. Addition of alcohols increases B22, indicating stronger protein-protein repulsion or weaker attraction. For the monohydric alcohols used in this study (methanol, ethanol, 1-propanol, n-butanol, iso-butanol and trifluoroethanol), B22 for lysozyme reaches a common plateau at approximately 5% (v/v) alcohol, while glycerol increases B22 more than monohydric alcohols. For a 0.05 M NaCl hen-egg lysozyme solution at pH 7, B22 increases from 2.4 x 10(-4) to 4.7 x 10(-4) ml mol/g2 upon addition of monohydric alcohols and to 5.8 x 10(-4) ml mol/g2 upon addition of glycerol. We describe the alcohol effect using a simple model that supplements the DLVO theory with an additional alcohol-dependent term representing orientation-averaged hydrophobic interactions. In this model, the increased lysozyme repulsive forces in the presence of monohydric alcohols are interpreted in terms of adsorption of alcohol molecules on hydrophobic sites on the protein surface. This adsorption reduces attractive hydrophobic protein-protein interactions. A thicker lysozyme hydration layer in aqueous glycerol solution can explain the glycerol-increased lysozyme-lysozyme repulsion.
醇类已被广泛用作蛋白质变性剂、沉淀剂和结晶试剂。我们通过使用静态光散射测量渗透压第二维里系数（B22），研究了醇类对水性鸡蛋溶菌酶自相互作用的影响。添加醇类会增加B22，表明蛋白质 - 蛋白质排斥增强或吸引力减弱。对于本研究中使用的一元醇（甲醇、乙醇、1 - 丙醇、正丁醇、异丁醇和三氟乙醇），溶菌酶的B22在约5%（v/v）的醇浓度时达到一个共同的平稳期，而甘油比一元醇更能增加B22。对于pH值为7的0.05 M NaCl鸡蛋溶菌酶溶液，添加一元醇后B22从2.4×10⁻⁴增加到4.7×10⁻⁴ ml mol/g²，添加甘油后增加到5.8×10⁻⁴ ml mol/g²。我们使用一个简单模型来描述醇类的作用，该模型在DLVO理论的基础上补充了一个额外的与醇相关的项，以表示取向平均的疏水相互作用。在这个模型中，一元醇存在时溶菌酶排斥力的增加被解释为醇分子吸附在蛋白质表面的疏水位点上。这种吸附减少了有吸引力的疏水蛋白质 - 蛋白质相互作用。水性甘油溶液中较厚的溶菌酶水化层可以解释甘油增加的溶菌酶 - 溶菌酶排斥作用。
