The reactions of neuroglobin with CO: Evidence for two forms of the ferrous protein
The reactions of neuroglobin with CO: Evidence for two forms of the ferrous protein
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DOI：
10.1016/j.jinorgbio.2006.03.009
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发表时间：
2006-08-01
影响因子：
3.9
通讯作者：
Brittain, Thomas
中科院分区：
文献类型：
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作者：
Fago, Angela;Mathews, Antony J.;Brittain, Thomas
正常的六配位亚铁形式的脑红蛋白通过取代与血红素相连的远端组氨酸残基与CO结合。我们用停流技术对该反应进行了详细研究。在所研究的所有波长下，反应时间过程都是复杂的。具体地说，与CO的反应发生在两个时间上可分离的阶段，每个阶段都表现出对CO浓度的双曲线依赖，表明它们都是由组氨酸被CO取代而产生的。分析观察到的速率作为CO浓度的函数，在pH 6.0-8.0的范围内测量，使我们能够确定在每个pH值下存在于溶液中的两种蛋白质的组氨酸-血红素配体结合和解离的速率。组氨酸结合和解离速率的pH依赖是复杂的，推导出的远端组氨酸结合的平衡常数也是复杂的。与每个反应相关联的光谱变化非常相似，并且与CO浓度无关，表明负责两个观察到的动力学过程的两种蛋白质形式在我们研究的时间尺度上不是平衡的。我们的数据表明，与许多其他血红素蛋白不同，由于血红素旋转紊乱，脑红蛋白与亚铁形式的配体显示出复杂的反应活性，正如之前报道的铁形式的蛋白质一样。(C)2006 Elsevier Inc.保留所有权利。
The normally hexa coordinate ferrous form of neuroglobin binds CO by replacement of the heme-linked distal histidine residue. We have studied this reaction in detail using stopped flow techniques. The reaction time courses are complex at all the wavelengths studied. Specifically the reaction with CO occurs in two temporally separable phases, each of which shows a hyperbolic dependence of rate on CO concentration, indicating they each arise from histidine replacement by CO. Analysis of the observed rates as a function of the CO concentration, measured in the pH range 6.0-8.0, allows us to determine both the rate of histidine-heme ligand binding and dissociation for each of the two forms of the protein present in solution at each pH value. The pH dependence of the histidine association and dissociation rates is complex, as are the derived equilibrium constants for distal histidine binding. The spectral change associated with each reaction phase is very similar and independent of the CO concentration, showing that the two protein forms responsible for the two observed kinetic processes are not in equilibrium on the time scale of our investigations. Our data suggests that, unlike many other heme proteins, neuroglobin displays complex reactivity with ligands in the ferrous form due to heme rotational disorder, as has previously been reported for the ferric form of the protein. (c) 2006 Elsevier Inc. All rights reserved.