Hemoglobin A: an electron paramagnetic resonance study of the effects of interchain contacts on the heme symmetry of high-spin and low-spin derivatives of ferric alpha chains.
Hemoglobin A: an electron paramagnetic resonance study of the effects of interchain contacts on the heme symmetry of high-spin and low-spin derivatives of ferric alpha chains.
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血红蛋白 A：电子顺磁共振研究链间接触对铁 α 链高自旋和低自旋衍生物血红素对称性的影响。
DOI：
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发表时间：
1969
影响因子：
11.1
通讯作者：
L. Kampa
中科院分区：
文献类型：
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作者：
J. Peisach;W. E. Blumberg;B. Wittenberg;J. Wittenberg;L. Kampa
血红蛋白是血液中与氧结合的血红素蛋白，由α和β两种类型的四个亚基组成。尽管分离后的蛋白质是抗磁性的，但通过氧化，它可以转化为各种顺磁性三价铁形式，表现出特定的电子顺磁共振 (EPR) 谱。使用电子顺磁共振，我们发现，当与母体四聚体中的三价铁β链结合时，分离的三价铁α链的血红素的对称性不同于这些相同亚基的血红素的对称性。与铁血红蛋白 A 相比，孤立的三价铁 α 链的高自旋形式显示出明显偏离四方对称性，其中所有四个链的铁环境都接近四方。血红素对称性的这种差异表明，血红蛋白四聚体中四方对称性的维持必须由α链由于与β链接触而呈现的构型来实现。当与四聚体分离时，α链的某些部分必须从已被β链稳定的构型发生物理位移。虽然在高自旋形式中可以看到单体和四聚体之间的对称性差异，但两种低自旋三价铁形式不存在这种差异。这里，铁的对称性主要由铁的直接配体环境决定，而不是由蛋白质的缔合状态决定。
Hemoglobin, the oxygen-binding heme protein of blood is composed of four subunits of two types, alpha and beta. Although the protein when isolated is diamagnetic, by oxidation it can be converted to various paramagnetic ferric forms exhibiting specific electron paramagnetic resonance (EPR) spectra. Using electron paramagnetic resonance, we have shown that the symmetry of the heme of isolated ferric alpha chains is different from that of the heme of these same subunits when associated with ferric beta chains in the parent tetramer. The high-spin form of the isolated ferric alpha chains shows a clearly resolved departure from tetragonal symmetry in contrast to ferrihemoglobin A, where the environment of the iron of all four chains is nearly tetragonal. This difference in heme symmetry suggests that the maintenance of tetragonal symmetry in the hemoglobin tetramer must be brought about by the configuration the alpha chains assume due to their contact with the beta chains. When isolated from the tetramer, some parts of the alpha chain must undergo physical displacement from a configuration that had been stabilized by the beta chains.Although differences in symmetry between monomer and tetramer are seen with high-spin forms, no such difference exists with two low-spin ferric forms. Here the symmetries of iron are primarily governed by the immediate ligand environment of the iron and not by the state of association of the protein.