SOLID LIQUID-PHASE BOUNDARIES OF LENS PROTEIN SOLUTIONS
SOLID LIQUID-PHASE BOUNDARIES OF LENS PROTEIN SOLUTIONS
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DOI：
10.1073/pnas.89.4.1214
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发表时间：
1992-02-15
影响因子：
11.1
通讯作者：
BENEDEK, GB
中科院分区：
文献类型：
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作者：
BERLAND, CR;THURSTON, GM;BENEDEK, GB
我们报告测量的固-液相边界，或液相线，三个纯小牛γ-晶状体蛋白的水溶液：γ-II，γ-IIIa，和γ-IIIb。我们还研究了天然γ-IV-晶状体蛋白小牛透镜蛋白溶液的液相线，其由85% γ-IVa/15% γ-IVb组成。在所有四种蛋白质中，液相线相边界的温度高于先前确定的液-液共存曲线。因此，在发生液-液相分离的浓度和温度范围内，蛋白质晶体相与蛋白质液体溶液相的共存相对于亚稳态分离的液相是化学稳定的。液相线的位置清楚地将这四种晶体蛋白分为两组：在温度> 70 ℃时液相线变平的：γ-IIIa和γ-IV，以及在温度< 50 ℃时液相线变平的：γ-II和γ-IIIb。我们已经分析了液相线的形式，通过使用特定的选择在溶液和固相的吉布斯自由能的结构。通过将两相之间平衡的热力学条件应用于所得的化学势，我们可以估计蛋白质和水结合到固相中时随温度变化的自由能变化。
We report measurement of the solid-liquid phase boundary, or liquidus line, for aqueous solutions of three pure calf gamma-crystallin proteins: gamma-II, gamma-IIIa, and gamma-IIIb. We also studied the liquidus line for solutions of native gamma-IV-crystallin calf lens protein, which consists of 85% gamma-IVa/15% gamma-IVb. In all four proteins the liquidus phase boundaries lie higher in temperature than the previously determined liquid-liquid coexistence curves. Thus, over the range of concentration and temperature for which liquid-liquid phase separation occurs, the coexistence of a protein crystal phase with a protein liquid solution phase is thermodynamically stable relative to the metastable separated liquid phases. The location of the liquidus lines clearly divides these four crystallin proteins into two groups: those in which liquidus lines flatten at temperatures > 70-degrees-C: gamma-IIIa and gamma-IV, and those in which liquidus lines flatten at temperatures < 50-degrees-C: gamma-II and gamma-IIIb. We have analyzed the form of the liquidus lines by using specific choices for the structures of the Gibbs free energy in solution and solid phases. By applying the thermodynamic conditions for equilibrium between the two phases to the resulting chemical potentials, we can estimate the temperature-dependent free energy change upon binding of protein and water into the solid phase.