The pH dependence of naturally occurring low-spin forms of methaemoglobin and metmyoglobin: an EPR study.
The pH dependence of naturally occurring low-spin forms of methaemoglobin and metmyoglobin: an EPR study.
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天然存在的低自旋形式高铁血红蛋白和高铁肌红蛋白的 pH 依赖性：一项 EPR 研究。
作者：
D. Svistunenko;M. Sharpe;P. Nicholls;C. Blenkinsop;N. Davies;J. Dunne;M. Wilson;C. Cooper
本文用电子顺磁共振（EPR）技术研究了低温下人高铁血红蛋白（metHb）和马高铁肌红蛋白（metMb）中的顺磁物质。aquometMb中的高自旋（HS）血红素信号具有比HS metHb信号更大的菱形失真。然而，个别线宽（g=6）是小于metMb比metHb，与不相同的信号从α和β血红蛋白亚基一致。metHb中存在三种低自旋（LS）血红素形式，而metMb只有两种。两种蛋白质中的主要LS形式是碱性物质（在第六配位位置具有OH（-））。次要的LS形式被分配到不同的组氨酸半色素平衡与正常的HS物种在低温下。当血红素被配体（如氟化物）结合时，LS形式消失，这确保在室温和25 K下100%占据HS状态。组氨酸半染色质的有效g-因子的微小差异被解释为远端组氨酸和血红素铁之间的不同距离。不同顺磁性物质相互转化的pH依赖性与pK为5.69（metHb）或6.12（metMb）的残基的质子化影响配体结合和从HS到LS形式的转化的模型一致。化学和光谱方面的考虑表明，该残基不太可能是近端或远端组氨酸。因此，我们提出了一个模型，其中质子化的这个遥远的氨基酸导致在铁网站的构象变化。在冷冻的人血中观察到相同的效果，表明这种效果可能具有生理意义。
The paramagnetic species in human metHb and horse metmyoglobin (metMb) have been studied at low temperature using EPR spectroscopy. The high-spin (HS) haem signal in aquometMb has a greater rhombic distortion than the HS metHb signal. Nevertheless, the individual line width (g=6) is smaller in metMb than in metHb, consistent with non-identical signals from the alpha and beta Hb subunits. Three low-spin (LS) haem forms are present in metHb, while metMb has only two. The major LS form in both proteins is the alkaline species (with OH(-) at the sixth co-ordination position). The minor LS forms are assigned to different histidine hemichromes in equilibrium with the normal HS species at low temperature. LS forms disappear when the haem is bound by a ligand, such as fluoride, which ensures 100% occupancy of the HS state both at room temperature and at 25 K. The small differences in effective g-factors of the histidine hemichromes are interpreted in terms of different distances between the distal histidine and haem iron. The pH dependence of the inter-conversion of the different paramagnetic species is consistent with a model whereby protonation of a residue with a pK of 5.69 (metHb) or 6.12 (metMb), affects ligand binding and transformation from the HS to the LS form. Chemical and spectroscopic considerations suggest that the residue is unlikely to be the proximal or distal histidine. We therefore propose a model where protonation of this distant amino acid causes a conformational change at the iron site. Identical effects are seen in frozen human blood, suggesting that this effect may have physiological significance.
研究肌红蛋白“开放”和“闭合”状态下的配体缔合和解离速率。
影响因子：
5.6
作者：
Tian,WD;Sage,JT;Champion,PM
通讯作者：
Champion,PM
影响因子：
3.9
作者：
Merryweather, J;Summers, F;Erman, JE
通讯作者：
Erman, JE