Ebel C, Eisenberg H, Ghirlando R
Institut de Biologie Structurale, CEA-CNRS, F-38027 Grenoble Cedex 1, France.
Biophys J. 2000 Jan;78(1):385-93. doi: 10.1016/S0006-3495(00)76601-X.
We have investigated the partial specific volumes (2) (ml/g), hydration, and cosolvent interactions of rabbit muscle aldolase by equilibrium sedimentation in the analytical ultracentrifuge and by direct density increment (partial differential/partial differentialc(2))(mu) measurements over a range of sugar concentrations and temperature. In a series of sugars increasing in size, glucose, sucrose, raffinose, and alpha-cyclodextrin, (partial differential/ partial differentialc(2))(mu) decreases linearly with the solvent density rho(0). These sugar cosolvents do not interact with the protein; however, the interaction parameter B(1) (g water/g protein) mildly increases with increasing sugar size. The experimental B(1) values are smaller than values calculated by excluded volume (rolling ball) considerations. B(1) relates to hydration in this and in other instances studied. It decreases with increasing temperature, leading to an increase in (2) due to reduced water of hydration electrostriction. The density increments (partial differential/ partial differentialc(2))(mu), however, decrease in concave up form in the case of glycerol and in concave down form for trehalose, leading to more complex behavior in the case of carbohydrates playing a biological role as osmolytes and antifreeze agents. A critical discussion, based on the thermodynamics of multicomponent solutions, is presented.
我们通过分析超速离心机中的平衡沉降以及在一系列糖浓度和温度范围内进行的直接密度增量（∂/∂c₂）μ测量，研究了兔肌肉醛缩酶的偏比容（ν₂）（ml/g）、水合作用和共溶剂相互作用。在一系列尺寸逐渐增大的糖（葡萄糖、蔗糖、棉子糖和α-环糊精）中，（∂/∂c₂）μ随溶剂密度ρ₀呈线性下降。这些糖共溶剂不与蛋白质相互作用；然而，相互作用参数B₁（g水/g蛋白质）随糖尺寸的增加略有增加。实验得到的B₁值小于通过排除体积（滚球）考虑计算得到的值。在本研究及其他研究实例中，B₁与水合作用相关。它随温度升高而降低，由于水合电致伸缩作用导致的结合水减少，使得ν₂增加。然而，甘油情况下密度增量（∂/∂c₂）μ呈凹形上升，海藻糖情况下呈凹形下降，这导致碳水化合物作为渗透剂和抗冻剂发挥生物学作用时表现出更复杂的行为。基于多组分溶液的热力学进行了批判性讨论。
