Calorimetric determination of the enthalpy change for the alpha-helix to coil transition of an alanine peptide in water.
Calorimetric determination of the enthalpy change for the alpha-helix to coil transition of an alanine peptide in water.
复制标题
量热法测定水中丙氨酸肽从 α 螺旋到卷曲转变的焓变。
DOI：
10.1073/pnas.88.7.2854
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发表时间：
1991
影响因子：
11.1
通讯作者：
Bolen,DW
中科院分区：
文献类型：
--
作者：
Scholtz,JM;Marqusee,S;Baldwin,RL;York,EJ;Stewart,JM;Santoro,M;Bolen,DW
用量热法测定了含有丙氨酸的50个氨基酸残基肽在水中由α -螺旋过渡到随机螺旋的焓变。螺旋形成焓是预测肽螺旋热展开曲线所需的基本参数之一，它是分析肽氢键的一个起点。δ H的实验不确定性反映了这样一个事实，即过渡曲线太宽，无法全部测量，这就排除了直接拟合基线的可能性。假设热容变化（Cp）为零，并允许基线在最低测得的Cp值处与过渡曲线相交，给出了展开H的下限，即每残基0.9千卡/摩尔。使用范霍夫方程和最小二乘拟合来确定更可能的基线，得到H = 1.3千卡/摩尔每个残留物。早前对聚赖氨酸和聚谷氨酸的研究得出每个残基1.1千卡/摩尔。这些研究以及我们目前的结果表明，侧链对H的影响很小。我们讨论了肽氢键显示相应的大H的可能性，以及对蛋白质稳定性的影响。
The enthalpy change (delta H) accompanying the alpha-helix to random coil transition in water has been determined calorimetrically for a 50-residue peptide of defined sequence that contains primarily alanine. The enthalpy of helix formation is one of the basic parameters needed to predict thermal unfolding curves for peptide helices and it provides a starting point for analysis of the peptide hydrogen bond. The experimental uncertainty in delta H reflects the fact that the transition curve is too broad to measure in its entirety, which precludes fitting the baselines directly. A lower limit for delta H of unfolding, 0.9 kcal/mol per residue, is given by assuming that the change in heat capacity (delta Cp) is zero, and allowing the baseline to intersect the transition curve at the lowest measured Cp value. Use of the van't Hoff equation plus least-squares fitting to determine a more probable baseline gives delta H = 1.3 kcal/mol per residue. Earlier studies of poly(L-lysine) and poly(L-glutamate) have given 1.1 kcal/mol per residue. Those investigations, along with our present result, suggest that the side chain has little effect on delta H. The possibility that the peptide hydrogen bond shows a correspondingly large delta H, and the implications for protein stability, are discussed.