PREFERENTIAL INTERACTIONS DETERMINE PROTEIN SOLUBILITY IN 3-COMPONENT SOLUTIONS - THE MGCL2 SYSTEM
PREFERENTIAL INTERACTIONS DETERMINE PROTEIN SOLUBILITY IN 3-COMPONENT SOLUTIONS - THE MGCL2 SYSTEM
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DOI：
10.1021/bi00459a036
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发表时间：
1990-02-20
期刊：
影响因子：
2.9
通讯作者：
TIMASHEFF, SN
中科院分区：
文献类型：
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作者：
ARAKAWA, T;BHAT, R;TIMASHEFF, SN
蛋白质溶解度和蛋白质与溶剂组分的优先相互作用之间的相关性进行了严格检查与MgCl 2水溶液作为溶剂系统。用三种蛋白质的优先相互作用和溶解度测量，β-乳球蛋白、牛血清白蛋白和溶菌酶导致类似的相互作用模式。在酸性pH（pH 2-3）和较低盐浓度（< 2 M）下，蛋白质优先水合，而在较高盐浓度下，相互作用是优先盐结合或低盐排斥。在pH 4.5-5，所有三种蛋白质表现出非常低的优先水合或优先结合的MgCl 2。这些结果进行了分析，在盐的结合和盐排斥之间的平衡归因于盐的水的表面张力的增加，这是不变的条件。结果表明，在高盐浓度下的盐结合的增加是质量作用的反映，而在酸性pH下的盐结合的减少是由于Mg 2+离子之间的静电排斥和蛋白质上的高净正电荷。蛋白质溶解度随溶剂条件的变化证实了优先相互作用模式。从水到盐溶液中的蛋白质溶液和沉淀物的转移自由能的计算显示盐浓度的平行依赖性。这表明蛋白质和溶剂组分之间的相互作用的性质在溶液和固体状态下是相同的，这意味着在沉淀期间蛋白质结构没有变化。分析的转移自由能和优先的相互作用参数的盐析，盐析，和弱离子结合的贡献，导致的结论是，当弱离子结合的贡献是小的，主要的蛋白质-盐的相互作用必须是优先的盐排斥最有可能引起的水的表面张力的增加，通过添加盐。如果蛋白质的结构要保持不变，其必然结果是蛋白质的盐析。
The correlation between protein solubility and the preferential interactions of proteins with solvent components was critically examined with aqueous MgCl2 as the solvent system. Preferential interaction and solubility measurements with three proteins, .beta.-lactoglobulin, bovine serum albumin, and lysozyme, resulted in similar patterns of interaction. At acid pH (pH 2-3) and lower salt concentrations (< 2 M), the proteins were preferentially hydrated, while at higher salt concentrations, the interaction was either that of preferential salt binding or low salt exclusion. At pH 4.5-5, all three proteins exhibited either very low preferential hydration or preferential binding of MgCl2. These results were analyzed in terms of the balance between salt binding and salt exclusion attributed to the increase in the surface tension of water by salts, which is invariant with conditions. It was shown that the increase in salt binding at high salt concentration is a reflection of mass action, while its decrease at acid pH is due to the electrostatic repulsion between Mg2+ ions and the high net positive charge on the protein. The preferential interaction pattern was paralleled by the variation of protein solubility with solvent conditions. Calculation of the transfer free energies from water to the salt solutions for proteins in solution and in the precipitate showed parallel dependencies on salt concentration. This indicates that the nature of interactions between proteins and solvent components is the same in solution and in the solid state, which implies no change in protein structure during precipitation. Analysis of the transfer free energies and preferential interaction parameter in terms of the salting-in, salting-out, and weak ion binding contributions has led to the conclusions that, when the weak ion binding contribution is small, the predominant protein-salt interaction must be that of preferential salt exclusion most probably caused by the increase of the surface tension of water by addition of the salt. A necessary consequence of this is salting-out of the protein, if the protein structure is to remain unaltered.