Vekilov Peter G
Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204, USA.
Ann N Y Acad Sci. 2009 Apr;1161:377-86. doi: 10.1111/j.1749-6632.2008.04318.x.
The Gibbs's definition of a phase assumes completely homogeneous composition, with fluctuations bringing about local variations of less than a few percent. We apply light scattering, atomic force microscopy, and other techniques to demonstrate that even solutions of a single protein of moderate concentration do not comply with Gibbs's definition of phase. In such solutions clusters of sizes from several tens to several hundred nanometers exist and have limited lifetimes. These clusters have a higher free energy than the protein solution, and their lifetime is determined by the barrier for their decay. The clusters affect the viscous and viscoelastic behavior of the solution and are an essential part of potential condensation and aggregation pathways. Since the clusters are observed in solutions of single proteins, they indicate that the proteins have an intrinsic propensity to form mesoscopic structures, which is probably utilized in the formation of the protein complexes in the cytosol. Cluster theories developed for colloid systems appear inapplicable to proteins due to the high level of implied Coulomb repulsion. The experimental evidence on the clusters suggests that their sizes are determined by the kinetics of growth and decay, and not by thermodynamics. A microscopic theory to account for stabilizing and destabilizing factors involving protein molecules and solvent inside the clusters has not yet been developed.
吉布斯对相的定义假定组成完全均匀，涨落导致的局部变化小于百分之几。我们应用光散射、原子力显微镜和其他技术来证明，即使是中等浓度的单一蛋白质溶液也不符合吉布斯对相的定义。在这类溶液中，存在着尺寸从几十到几百纳米不等的聚集体，且它们的寿命有限。这些聚集体的自由能高于蛋白质溶液，其寿命由它们衰变的势垒决定。聚集体会影响溶液的粘性和粘弹性行为，并且是潜在的凝聚和聚集途径的重要组成部分。由于在单一蛋白质溶液中观察到了聚集体，这表明蛋白质具有形成介观结构的内在倾向，这种倾向可能在细胞溶质中蛋白质复合物的形成过程中发挥作用。由于隐含的库仑排斥作用程度很高，为胶体系统发展的聚集体理论似乎不适用于蛋白质。关于聚集体的实验证据表明，它们的尺寸由生长和衰变动力学决定，而非由热力学决定。目前尚未建立一个微观理论来解释涉及聚集体内蛋白质分子和溶剂的稳定和不稳定因素。
