Ibanez V S, Herskovits T T
Biochemistry. 1976 Dec 28;15(26):5708-14. doi: 10.1021/bi00671a005.
The effects of the aliphatic acid series of salts, formate, acetate, propionate, butyrate, valarate, and caproate, on the conformation of sperm whale myoglobin, human hemoglobin A, and horse heart cytochrome c were investigated by spectral measurements in the Soret region, optical rotation, and intrinsic viscosity measurements. The effectiveness of the aliphatic acid salts as unfolding reagents for proteins is found to increase with increasing hydrocarbon content of the alkyl chains of the salts, which is analogous in behavior to effects of the urea, amide, and alcohol series of protein denaturants. The denaturation midpoints, Sm, as a function of the unfolding reagent were analyzed using the equations of Peller (Peller, L. (1959), J. Phys, Chem- 63, 1199) and Flory (Flory, P.J. (1957), J. Cell. Comp. Physiol. 49, 175) with binding constants based in part on the Scherage-Nemethy theory of hydrophobic bonding or evaluated from free-energy transfer data of nonpolar amino acid side chains from aqueous to nonaqueous solvents. The summation of the polar KP and hydrophobic KHphi contributions of solvent to protein amino acid side chain interactions were found to give best account of the protein denaturation data. Intrinsic viscosity and optical rotation data obtained on hemoglobin and myoglobin at high salt concentrations, above the unfolding transition regions, indicate that the product of denaturation by the aliphatic acid salts is less unfolded than in 6 M guanidine hydrochloride solutions. Residual elements of the helical regions of the proteins seem to either escape unfolding or are reformed at high concentrations of the denaturing salts.
通过在索雷特区域的光谱测量、旋光性和特性粘度测量，研究了脂肪酸系列盐（甲酸盐、乙酸盐、丙酸盐、丁酸盐、戊酸盐和己酸盐）对抹香鲸肌红蛋白、人血红蛋白A和马心细胞色素c构象的影响。发现脂肪酸盐作为蛋白质展开剂的有效性随着盐烷基链烃含量的增加而增加，这在行为上类似于尿素、酰胺和醇系列蛋白质变性剂的影响。使用佩勒（佩勒，L.（1959年），《物理化学杂志》-63，1199）和弗洛里（弗洛里，P.J.（1957年），《细胞与比较生理学杂志》49，175）的方程，结合部分基于疏水键合的谢拉热-内梅蒂理论的结合常数或从非极性氨基酸侧链从水相到非水相溶剂的自由能转移数据评估的结合常数，分析了作为展开剂函数的变性中点Sm。发现溶剂对蛋白质氨基酸侧链相互作用的极性KP和疏水KHphi贡献的总和最能解释蛋白质变性数据。在高于展开转变区域的高盐浓度下对血红蛋白和肌红蛋白获得的特性粘度和旋光性数据表明，脂肪酸盐变性的产物比在6M盐酸胍溶液中展开程度更低。蛋白质螺旋区域的残余部分似乎要么避免展开，要么在高浓度变性盐下重新形成。
