电离辐射对血红蛋白的影响：岩手血红蛋白的氧衍生物。

Effect of ionizing radiation on haemoglobin: the oxy-derivative of haemoglobin Iwate.

作者信息

Bartlett M N, Stephenson J M, Symons M C

机构信息

Department of Chemistry, University of Leicester, U.K.

出版信息

Proc R Soc Lond B Biol Sci. 1989 Nov 22;238(1291):103-12. doi: 10.1098/rspb.1989.0069.

DOI:10.1098/rspb.1989.0069

PMID:2575747

Abstract

It is well established that exposure of oxyhaemoglobin to ionizing radiation results in remarkably selective electron addition to the (FeO2) unit, giving a novel species, (FeO2)-, in which the extra electron is largely localized on iron and dioxygen. This work has now been extended to haemoglobin (Hb.) Iwate. The haemoglobin M. Iwate used is a mutant haemoglobin having only Fe(III) alpha-chains by oxy beta-chains (alpha 2 Met beta 2 oxy). The haem iron atoms in the alpha-chains are coordinated in the fifth site by a proximal tyrosine in place of histidine. This unit is a high-spin Fe(III) with axial symmetry and prominent electron spin resonance (ESR) features in the g = 6 and g = 2 regions. On exposure to 60Co gamma-rays at 77 K, efficient electron addition occurred at both types of iron centre, giving Fe(II) and (FeO2)- units. The former was monitored by the decrease of the g = 6 feature for Fe(III) and the latter by the growth of g-features at 2.254 (gx), 2.149 (gy) and 1.967 (gz). These values are close to those for the FeO2- centre formed in the beta-chains of normal oxyhaemoglobin. On annealing above 77 K, two changes occurred: first there was a small but clear increase in gx and gy, followed by a marked reduction in gx and gy giving g-values close to those for the centre formed directly in the alpha-chains of the normal protein. Finally, this intermediate species gave a centre having gx = 2.310, gy = 2.180 and gz = 1.935. These values are typical of low-spin Fe(III) haemoglobin and are assigned to the protonated complex, Fe(III)O2H. Ultimately at ca. room temperature, this was converted into the high-spin, met-form, with a gain in the g = 6 feature. These results established that the beta-chain centre in Hb. Iwate behave in the same way as isolated beta-chains. They also confirm that electron addition to the oxy-units is facile, even in the presence of Fe(III) units in each tetramer. The results also confirm that electron capture to give (FeO2)- units is not followed by internal electron-transfer to give Fe(II) from the Fe(III) centres in the alpha-chains.

摘要

众所周知，氧合血红蛋白暴露于电离辐射下会导致（FeO₂）单元显著选择性地添加电子，生成一种新物种（FeO₂）⁻，其中额外的电子主要定域在铁和双氧上。这项工作现已扩展到岩手血红蛋白（Hb.）。所使用的岩手血红蛋白M是一种突变血红蛋白，其α链仅含Fe(III)，β链为氧合状态（α₂Metβ₂氧合）。α链中的血红素铁原子在第五配位位点由近端酪氨酸取代组氨酸进行配位。该单元是具有轴向对称性的高自旋Fe(III)，在g = 6和g = 2区域具有显著的电子自旋共振（ESR）特征。在77 K下暴露于⁶⁰Coγ射线时，两种类型的铁中心均发生了有效的电子添加，生成了Fe(II)和（FeO₂）⁻单元。前者通过Fe(III)的g = 6特征的减弱来监测，后者通过2.254（gx）、2.149（gy）和1.967（gz）处g特征的增长来监测。这些值与正常氧合血红蛋白β链中形成的FeO₂⁻中心的值接近。在高于77 K退火时，发生了两个变化：首先gx和gy有小但明显的增加，随后gx和gy显著降低，其g值接近正常蛋白质α链中直接形成的中心的值。最后，这个中间物种产生了一个gx = 2.310、gy = 2.180和gz = 1.935的中心。这些值是低自旋Fe(III)血红蛋白的典型值，被归属于质子化复合物Fe(III)O₂H。最终在约室温下，它转变为高自旋的高铁形式，g = 6特征增强。这些结果表明，岩手血红蛋白中的β链中心与分离的β链行为相同。它们还证实，即使在每个四聚体中存在Fe(III)单元的情况下，向氧合单元添加电子也很容易。结果还证实，产生（FeO₂）⁻单元的电子捕获之后不会发生内部电子转移，从α链中的Fe(III)中心生成Fe(II)。