CRYSTALS OF HEMOGLOBIN WITH THE T-QUARTERNARY STRUCTURE BIND OXYGEN NONCOOPERATIVELY WITH NO BOHR EFFECT
CRYSTALS OF HEMOGLOBIN WITH THE T-QUARTERNARY STRUCTURE BIND OXYGEN NONCOOPERATIVELY WITH NO BOHR EFFECT
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DOI：
10.1038/351416a0
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发表时间：
1991-05-30
期刊：
影响因子：
64.8
通讯作者：
EATON, WA
中科院分区：
文献类型：
--
作者：
MOZZARELLI, A;RIVETTI, C;EATON, WA
血红蛋白的结构和功能之间的关系主要是通过比较其X射线晶体结构和其在溶液1-11中的功能来研究的。 为了进行直接比较，我们研究了血红蛋白在单晶中的功能特性，这种方法一直是几种酶机制研究的重要组成部分12，13。 在这里，我们报告在聚乙二醇溶液中生长的人血红蛋白单晶的氧结合。 与在浓盐溶液中形成的血红蛋白晶体不同，血红蛋白晶体在氧化时破裂并变得无序14-16，在聚乙二醇中生长的晶体保持完整。 X射线研究表明，在pH 7.0时，该晶体中血红蛋白的T（脱氧）四级结构在大气氧压下保持不变，并且盐桥不断裂17-19。 我们发现显着的差异之间的氧结合血红蛋白在这个晶体和血红蛋白在溶液中。 不仅是氧的晶体不合作，但氧亲和力是独立的pH值范围内6.0-8.5，是远远低于溶液中的T状态。 在四级结构没有变化的情况下缺乏协同性由Monod，Wyman和Changeux 1，5的双态变构模型预测。 佩鲁茨的立体化学机制预测，在没有盐桥断裂的情况下不存在玻尔效应2，4，9-11。 与X射线结果氧仅与α-血红素结合相反，我们的测量表明α-血红素仅具有比β-血红素略高的亲和力。
THE relationship between the structure and function of haemoglobin has mainly been studied by comparing its X-ray crystal structures with its function in solutions 1-11. To make a direct comparison we have studied the functional properties of haemoglobin in single crystals, an approach that has been an important part of the investigation of several enzyme mechanisms 12, 13. Here we report on the oxygen binding by single crystals of human haemoglobin grown in solutions of polyethylene glycol. Unlike haemoglobin crystals formed in concentrated salt solution, which crack and become disordered on oxygenation 14-16, crystals grown in polyethylene glycol remain intact. X-ray studies have shown that the T (deoxy) quaternary structure of haemoglobin in this crystal at pH 7.0 is maintained at atmospheric oxygen pressure, and that the salt-bridges are not broken 17-19. We find striking differences between oxygen binding by haemoglobin in this crystal and by haemoglobin in solution. Not only is oxygenation of the crystal noncooperative, but the oxygen affinity is independent of pH in the range 6.0-8.5, and is much lower than that of the T state in solution. The lack of cooperativity without a change in quaternary structure is predicted by the two-state allosteric model of Monod, Wyman and Changeux 1, 5. The absence of a Bohr effect without breakage of salt-bridges is predicted by Perutz's stereochemical mechanism 2, 4, 9-11. In contrast to the X-ray result that oxygen binds only to the alpha-haems, our measurements show that the alpha-haems have only a slightly higher affinity than the beta-haems.