Yamasaki M, Yano H, Aoki K
Daiichi College of Pharmaceutical Sciences, Fukuoka, Japan.
Int J Biol Macromol. 1991 Dec;13(6):322-8. doi: 10.1016/0141-8130(91)90012-j.
Using defatted and SH-blocked bovine serum albumin (BSA), measurements of differential scanning calorimetry (d.s.c.) have been made mainly in NaSCN solution. BSA undergoes a heat-induced conformational transition in a particular range of pH and ionic strength and is separated into two thermally independent units, each of which has different thermostability in acidic and alkaline pH regions. Comparisons were made of the pH dependencies of the enthalpy of thermal denaturation (delta H) and the temperature of thermal denaturation (Td) in 0.01 M NaSCN with those in 0.01 M NaCl. It has been found that the stabilizing effect of NaSCN on BSA is larger than that of NaCl at pH 3.5-8, and that the heat-induced transition occurs by the electrostatic repulsive forces among the positively charged amino acid residues in a segment Arg 184-Arg 216 containing Trp 212 and the primary binding sites of anions. At ionic strength 0.01, the relative effectiveness of anions in suppressing the heat-induced transition and increasing the thermostability of BSA follows the order ClO4- - greater than or equal to SCN- greater than I- greater than SO4(2-) greater than Br- greater than Cl-. At ionic strength 0.1, the heat-induced transition is suppressing in all the salt solutions, and a Td increase follows the order ClO4- greater than or equal to SCN- greater than I- greater than Br- greater than Cl- greater than or equal to SO4(2-). Thus, the highly chaotropic ions thermostabilize BSA more markedly than kosmotropic ions in the low and moderate salt concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
使用脱脂且巯基封闭的牛血清白蛋白（BSA），主要在硫氰酸钠（NaSCN）溶液中进行了差示扫描量热法（d.s.c.）测量。BSA在特定的pH值和离子强度范围内会发生热诱导构象转变，并被分离成两个热独立单元，每个单元在酸性和碱性pH区域具有不同的热稳定性。比较了在0.01 M NaSCN和0.01 M NaCl中热变性焓（ΔH）和热变性温度（Td）对pH的依赖性。发现在pH 3.5 - 8时，NaSCN对BSA的稳定作用大于NaCl，并且热诱导转变是由包含色氨酸212和阴离子主要结合位点的184位精氨酸 - 216位精氨酸片段中带正电的氨基酸残基之间的静电排斥力引起的。在离子强度为0.01时，阴离子抑制热诱导转变并提高BSA热稳定性的相对有效性顺序为：高氯酸根离子≥硫氰酸根离子＞碘离子＞硫酸根离子＞溴离子＞氯离子。在离子强度为0.1时，所有盐溶液中热诱导转变均受到抑制，热变性温度升高的顺序为：高氯酸根离子≥硫氰酸根离子＞碘离子＞溴离子＞氯离子≥硫酸根离子。因此，在低和中等盐浓度下，高度离液序列高的离子比促溶剂离子更显著地使BSA热稳定。（摘要截于250字）
