UNFOLDING FREE-ENERGY CHANGES DETERMINED BY THE LINEAR EXTRAPOLATION METHOD .2. INCORPORATION OF DELTA-G-DEGREES-N-U VALUES IN A THERMODYNAMIC CYCLE
UNFOLDING FREE-ENERGY CHANGES DETERMINED BY THE LINEAR EXTRAPOLATION METHOD .2. INCORPORATION OF DELTA-G-DEGREES-N-U VALUES IN A THERMODYNAMIC CYCLE
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DOI：
10.1021/bi00421a015
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发表时间：
1988-10-18
期刊：
影响因子：
2.9
通讯作者：
SANTORO, MM
中科院分区：
文献类型：
--
作者：
BOLEN, DW;SANTORO, MM
使用线性外推法来评估pH 6.0下苯甲磺酰基胰凝乳蛋白酶（PMS-Ct）的解折叠自由能变化（Δ G ° N-U）。使用尿素和氯化胍作为变性剂的差光谱数据的非线性最小二乘拟合给出了Δ G ° N-U和Δ G ° N-U的相同值。你...后者是在变性剂浓度为零的极限下，蛋白质的天然和未折叠形式之间的消光系数差。这些参数与溶剂性质的独立性强烈表明它们是单独的蛋白质的特征性质。将在pH 6.0和4.0下的Δ G ° N-U数据（其在蛋白质的稳定性方面相差超过100倍）并入涉及自由能变化的热力学循环中，用于从pH 4.0至6.0滴定天然和未折叠的PMS-Ct。该循环的目的是测试通过使用线性外推法获得的Δ G ° N-U是否表现出状态的热力学函数所需的特性。在误差范围内，发现热力学循环适应PMS-Ct在pH 4.0和6.0下获得的Δ G ° N-U量。
The linear extrapolation method was used to evaluate the unfolding free energy changes (.DELTA.G.degree.N-U) for phenylmethanesulfonyl chymotrypsin (PMS-Ct) at pH 6.0. The nonlinear least-squares fits of difference spectral data using urea and guanidinium chloride as denaturants gave identical values for .DELTA.G.degree.N-U and .DELTA..epsilon..degree.U, the latter being extinction coefficient differences between native and unfolded forms of the protein in the limit of zero concentration of denaturant. The independence of these parameters from the nature of solvent suggests strongly that they are characteristic properties of the protein alone. The .DELTA.G.degree.N-U data t pH 6.0 and 4.0, which differ by more than 100-fold in stability of the protein, were incorporated into a thermodynamic cycle involving free energy changes for titration of native and unfolded PMS-Ct from pH 4.0 to 6.0. The purpose of the cycle was to test whether .DELTA.G.degree.N-U obtained by use of the linear extrapolation method exhibits the characteristics required of a thermodynamic function of state. Within error, the thermodynamic cycle was found to accommodate the .DELTA.G.degree.N-U quantities obtained at pH 4.0 adn 6.0 for PMS-Ct.