THERMODYNAMIC ANALYSIS OF CARBON-MONOXIDE BINDING BY HEMOGLOBIN TROUT-I
THERMODYNAMIC ANALYSIS OF CARBON-MONOXIDE BINDING BY HEMOGLOBIN TROUT-I
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DOI：
10.1016/0301-4622(79)85006-1
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发表时间：
1979-01-01
影响因子：
3.8
通讯作者：
GILL, SJ
中科院分区：
文献类型：
--
作者：
BARISAS, BG;GILL, SJ
25度的量热测量。测定了Hb鳟鱼1号的CO结合差热C和蛋白质在4℃下的CO结合等温线。摄氏20度。C.通过严格的统计技术同时处理这些数据集，可以对Adair和Monod， Wyman, Changeux （MWC）模型的所有热力学参数进行评估。该Hb表现出不同寻常的温度依赖性协同性。在Adair形式中，配体结合的连续步骤的自由能变化越来越有利，与这些步骤的焓变化越来越负几乎线性平行。这导致随着温度的降低，所观察到的协同性增强。对于MWC的情况，降低温度增加了相对于未结合的R态的T态的稳定性。R跃迁为29.4 kcal mol-1。同时，R型连接相对于T的优势性增强，因为R型连接比T的放热多14.1 kcal (mol CO)-1。这两种相反作用之间的平衡是在低温下增加配体的结合协同性。MWC和Adair模型预测的Hill系数的温度依赖性在低温和中温下是相同的，但有趣的是，在高温下会显示出强烈的分歧，在高温下，Adair的情况下是负协同性，而MWC的情况下是正协同性。
Calorimetric measurements at 25.degree. C of the differential heat of CO binding by Hb trout I were examined together with the CO binding isotherms for the protein at 4.degree. C and 20.degree. C. Simultaneous treatment of these data sets by a statistically rigorous technique permitted evaluation of all the thermodynamic parameters for both the Adair and the Monod, Wyman, Changeux (MWC) models. The unusual temperature dependent cooperativity which this Hb exhibits were shown. In the Adair formalism the increasingly favorable free energy change for successive steps of ligand binding were nearly linearly paralleled by increasingly negative enthalpy changes for these steps. This caused the enhanced cooperativity observed as the temperature was decreased. For the MWC case, lowering the temperature increased the stability of the unligated T state relative to the unligated R state since the enthalpy of the T .fwdarw. R transition was 29.4 kcal mol-1. Simultaneously, the favorability of ligating R forms relative to T was enhanced since R form ligation was 14.1 kcal (mol CO)-1 more exothermic than that of T. The balance between these opposing effects was to increase ligand binding cooperativity at low temperatures. The predicted temperature dependence of the Hill coefficient for the MWC and Adair models was identical at low and intermediate temperatures but, interestingly, would show a strong divergence at high temperatures where negative cooperativity is suggested for the Adair case and positive cooperativity for the MWC case.