Calorimetric studies of interactions between low molecular weight salts and bovine serum albumin in water at pH values below and above the isoionic point
Calorimetric studies of interactions between low molecular weight salts and bovine serum albumin in water at pH values below and above the isoionic point
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DOI：
10.1016/j.molliq.2017.10.105
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发表时间：
2018-11-15
影响因子：
6
通讯作者：
Luksic, Miha
中科院分区：
文献类型：
--
作者：
Janc, Tadeja;Vlachy, Vojko;Luksic, Miha
采用等温滴定量热法测定了牛血清白蛋白（BSA）在含有几种低分子量盐的缓冲水溶液中的混合焓（Δ H-mix）对温度和盐浓度的依赖性。使用三种缓冲液：乙酸盐（pH = 4.0）、MOPS（7.2）和硼酸盐（9.2）。由于BSA的等离子点在pI约4.7处，因此BSA在乙酸盐缓冲液中的净电荷为正（约+20），而在其他两种缓冲液中为负（MOPS中约为-15，硼酸盐中约为-25）。大多数记录的热效应是放热的，而只有在pH = 9.2时，观察到BSA与LiCl，NaCl和KCl混合后的弱吸热效应。对于所有缓冲溶液，钠盐的Δ H-混合物的绝对值遵循以下顺序：NaCl < NaBr <NaNO 3 <NaI < NaSCN，这是阴离子的逆霍夫迈斯特系列。的影响的幅度是最大的醋酸盐缓冲液中，并随着溶液的pH值的增加而降低。虽然在所有pH值下改变所添加的盐的阴离子的效果都非常明显，但阳离子（LiCl、NaCl、KCl、RbCl和CsCl盐）的效果很弱。对于pH > pI获得的结果的最有趣的特征是，Δ H-混合物对阴离子（对净BSA电荷的共离子）比对阳离子种类敏感得多。这表明，即使在蛋白质的净电荷为负的pH值下，阴离子与BSA的相互作用也相当强烈。我们发现，在高加成盐的Δ H-m（i）x与相应的盐阴离子的水合焓很好地相关。这一发现表明，与以前的一些研究一致，对Delta H混合物的放热贡献的一部分源自蛋白质-盐相互作用后的水合变化。理论分析，基于原始模型的高度不对称的电解质溶液中解决的平均球近似，被用来估计库仑效应混合。(C)2017年爱思唯尔。All rights reserved.
Isothermal titration calorimetry was used to determine the temperature and salt concentration dependence of the enthalpy of mixing, Delta H-mix, of bovine serum albumin (BSA) in aqueous buffer solutions with several low molecular weight salts. Three buffers were used: acetate (pH = 4.0), MOPS (7.2), and borate (9.2). Since the isoionic point of BSA is at pI approximate to 4.7, the net charge of BSA in acetate buffer was positive ( approximate to +20), while in the other two buffer solutions it was negative (approximate to-15 in MOPS and approximate to-25 in borate). The majority of the recorded heat effects were exothermic, while only at pH = 9.2 a weak endothermic effect upon mixing BSA with LiCl, NaCl, and KCl was observed. For all buffer solutions the absolute values of Delta H-mix of sodium salts followed the order: NaCl < NaBr < NaNO3 < Nal < NaSCN, which is the reverse Hofmeister series for anions. The magnitude of the effects was the largest in acetate buffer and decreased with an increasing pH value of the solution. While the effect of varying the anion of the added salts was strongly pronounced at all pH values, the effect of the cation (Licl, NaCl, KCl, RbCl and CsCl salts) was weak. The most interesting feature of the results obtained for pH > pI was the fact that Delta H-mix were considerably more sensitive to the anion (co-ion to the net BSA charge) than to the cation species. This indicated that anions interacted quite strongly with the BSA even at pH values where the net charge of the protein was negative. We showed that Delta H-m(i)x at high addition of salts correlated well with the enthalpy of hydration of the corresponding salt anion. This finding suggested, consistently with some previous studies, that a part of the exothermic contribution to Delta H-mix originated from the hydration changes upon the protein-salt interaction. Theoretical analysis, based on the primitive model of highly asymmetric electrolyte solutions solved within the mean spherical approximation, was used to estimate Coulomb effects upon mixing. (C) 2017 Elsevier By. All rights reserved.