Davies M J
Department of Chemistry, University of York, Heslington, U.K.
Free Radic Res Commun. 1990;10(6):361-70. doi: 10.3109/10715769009149905.
The reaction of metmyoglobin with equimolar concentrations of hydrogen peroxide has been studied using both electron spin resonance (e.s.r.) and optical spectroscopy. Using the former technique a strong anisotropic e.s.r. signal is observed, in the presence of the spin trap DMPO, which decays relatively rapidly. This previously unobserved signal, which is also observed on reaction of metmyoglobin with a number of other powerful oxidants (peracetic acid, 3-chloroperoxybenzoic acid, monoperoxyphthalic acid, iodosyl benzene, tBuOOH and cumene hydroperoxide) is assigned to a slowly-tumbling, metmyoglobin-derived, spin adduct. The parameters of this signal (aN 1.45, aH 0.83 mT) are consistent with the trapped radical having a heteroatom centre: this is believed to be oxygen. The concentration of this species is not affected by compounds such as 2-deoxyribose, mannitol and phenylalanine which are all efficient hydroxyl radical scavengers, demonstrating that the formation of this radical is not due to reaction of "free" HO. generated by breakdown of H2O2 by released iron ions. The concentration of this species is however decreased by desferal, ascorbate. Trolox C, salicylate and, to a lesser extent, linoleic acid; with the first three of these compounds further substrate-derived radicals are also observed. Examination of similar reaction systems (though in the absence of DMPO) by optical spectroscopy shows that the myoglobin (IV) species is formed and that this species behaves in a somewhat different manner with these added compounds. These results suggest that the radical trapped in the e.s.r. experiments is a myoglobin-derived species, probably a tyrosine peroxyl radical, arising from oxidative damage to the globin moiety. The diminution of both the e.s.r. signal of the spin adduct and the optical absorption of the myoglobin (IV) species in the presence of linoleic acid suggests that these myoglobin-derived species can initiate oxidative damage but that this process can be ameliorated by the presence of a number of water-soluble compounds such as ascorbate, Trolox C, desferal and salicylate.
利用电子自旋共振（e.s.r.）和光谱学研究了高铁肌红蛋白与等摩尔浓度过氧化氢的反应。使用前一种技术，在自旋捕获剂DMPO存在下观察到一个强各向异性的e.s.r.信号，该信号衰减相对较快。这个以前未观察到的信号，在高铁肌红蛋白与许多其他强氧化剂（过氧乙酸、3-氯过氧苯甲酸、单过氧邻苯二甲酸、亚碘酰苯、叔丁基过氧化氢和氢过氧化异丙苯）反应时也能观察到，被归因于一种缓慢翻滚的、源自高铁肌红蛋白的自旋加合物。该信号的参数（aN 1.45，aH 0.83 mT）与捕获的自由基具有杂原子中心一致：据信该杂原子中心为氧。该物种的浓度不受2-脱氧核糖、甘露醇和苯丙氨酸等化合物的影响，这些化合物都是有效的羟基自由基清除剂，这表明该自由基的形成不是由于释放的铁离子分解过氧化氢产生的“游离”HO反应所致。然而，去铁胺、抗坏血酸盐、生育三烯酚C、水杨酸盐以及程度较轻的亚油酸会降低该物种的浓度；对于前三种化合物，还观察到了进一步的源自底物的自由基。通过光谱学检查类似的反应体系（尽管不存在DMPO）表明形成了肌红蛋白（IV）物种，并且该物种与这些添加化合物的反应方式有所不同。这些结果表明，在e.s.r.实验中捕获的自由基是一种源自肌红蛋白的物种，可能是酪氨酸过氧自由基，由球蛋白部分的氧化损伤产生。在亚油酸存在下，自旋加合物（spin adduct）的e.s.r.信号和肌红蛋白（IV）物种的光吸收都减弱，这表明这些源自肌红蛋白的物种可以引发氧化损伤，但许多水溶性化合物如抗坏血酸盐、生育三烯酚C、去铁胺和水杨酸盐的存在可以改善这一过程。
