SALTING-OUT OF AQUEOUS PROTEINS - PHASE-EQUILIBRIA AND INTERMOLECULAR POTENTIALS
SALTING-OUT OF AQUEOUS PROTEINS - PHASE-EQUILIBRIA AND INTERMOLECULAR POTENTIALS
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DOI：
10.1002/aic.690410430
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发表时间：
1995-04-01
期刊：
影响因子：
3.7
通讯作者：
PRAUSNITZ, JM
中科院分区：
文献类型：
--
作者：
COEN, CJ;BLANCH, HW;PRAUSNITZ, JM
本文报道了溶菌酶和α-糜蛋白酶从浓硫酸铵溶液中的盐析相平衡。上清液和密相蛋白质的浓度和由此产生的蛋白质分配系数作为溶液pH值和离子强度的函数。与三价盐（柠檬酸钠）的相平衡证实，离子强度，而不是盐浓度是描述相平衡的适当变量。用低角激光光散射（LALLS）方法研究了溶菌酶和α-糜蛋白酶的混合物的盐析行为，得到了盐析行为的分子热力学参数。在0.01和1.0 M离子强度下，在电解质水溶液中稀释糜蛋白酶浓度的pH范围内报告了来自LALLS的渗透第二病毒系数。有效Hamaker常数，从实验渗透第二维里系数回归，确定模型的蛋白质-蛋白质的平均力的潜力。除了排除体积，分散和屏蔽电荷-电荷电位，蛋白质-蛋白质相互作用的描述包括吸引电荷-偶极子和偶极子-偶极子电位以及在高盐浓度下变得重要的吸引力-吸引力电位。蛋白质偶极-偶极电位需要考虑到所观察到的pH依赖性的渗透第二维里系数，特别是在低离子强度。
Salting-out phase equilibria ale reported for lysozyme and alpha-chymotrypsin from concentrated ammonium-sulfate solutions. Supernatant and dense-phase protein concentrations and the resulting protein partition coefficients are given as a function of solution pH and ionic strength. Phase equilibria with a trivalent salt (sodium citrate) confirm that ionic strength, rather than salt concentration is the appropriate variable describing phase equilibria. The salting-out behavior of a mixture of an aqueous lysozyme and alpha-chymotrypsin is independent of the presence of the other protein.Parameters for a molecular-thermodynamic description of salting-out behavior are obtained from low-angle laser-light scattering (LALLS). Osmotic second viral coefficients from LALLS are reported over a range of pH for dilute chymotrypsin concentrations in aqueous electrolyte solutions at 0.01 and 1.0 M ionic strengths. Effective Hamaker constants, regressed from experimental osmotic second virial coefficients, are determined for models of the protein-protein potential of mean force. In addition to excluded volume, dispersion and shielded charge-charge potentials, the description of protein-protein interactions includes attractive charge-dipole and dipole-dipole potentials as well as an osmotic-attraction potential that becomes important at high salt concentrations. Protein dipole-dipole potentials are required to account for the observed pH dependence of osmotic second virial coefficients, especially at low ionic strength.