Nauser Thomas, Gebicki Janusz M
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology , Zurich CH8093, Switzerland.
Department of Biological Sciences, Macquarie University , Sydney, New South Wales 2109, Australia.
Chem Res Toxicol. 2017 Sep 18;30(9):1702-1710. doi: 10.1021/acs.chemrestox.7b00160. Epub 2017 Aug 29.
The principal initial biological targets of free radicals formed under conditions of oxidative stress are the proteins. The most common products of the interaction are carbon-centered alkyl radicals which react rapidly with oxygen to form peroxyl radicals and hydroperoxides. All these species are reactive, capable of propagating the free radical damage to enzymes, nucleic acids, lipids, and endogenous antioxidants, leading finally to the pathologies associated with oxidative stress. The best chance of preventing this chain of damage is in early repair of the protein radicals by antioxidants. Estimate of the effectiveness of the physiologically significant antioxidants requires knowledge of the antioxidant tissue concentrations and rate constants of their reaction with protein radicals. Previous studies by pulse radiolysis have shown that only ascorbate can repair the Trp and Tyr protein radicals before they form peroxyl radicals under physiological concentrations of oxygen. We have now extended this work to other protein C-centered radicals generated by hydroxyl radicals because these and many other free radicals formed under oxidative stress can produce secondary radicals on virtually any amino acid residue. Pulse radiolysis identified two classes of rate constants for reactions of protein radicals with ascorbate, a faster one in the range (9-60) × 10 M s and a slow one with a range of (0.5-2) × 10 M s. These results show that ascorbate can prevent further reactions of protein radicals only in the few human tissues where its concentration exceeds about 2.5 mM.
在氧化应激条件下形成的自由基，其主要的初始生物学靶点是蛋白质。相互作用最常见的产物是以碳为中心的烷基自由基，它们能迅速与氧反应形成过氧自由基和氢过氧化物。所有这些物质都具有反应活性，能够将自由基损伤传播到酶、核酸、脂质和内源性抗氧化剂上，最终导致与氧化应激相关的病变。预防这种损伤链的最佳机会在于通过抗氧化剂对蛋白质自由基进行早期修复。评估具有生理意义的抗氧化剂的有效性，需要了解抗氧化剂在组织中的浓度及其与蛋白质自由基反应的速率常数。先前通过脉冲辐解进行的研究表明，在生理氧浓度下，只有抗坏血酸能够在色氨酸和酪氨酸蛋白自由基形成过氧自由基之前对其进行修复。我们现在已将这项工作扩展到由羟基自由基产生的其他以蛋白质碳为中心的自由基，因为在氧化应激下形成的这些自由基以及许多其他自由基，几乎可以在任何氨基酸残基上产生次级自由基。脉冲辐解确定了蛋白质自由基与抗坏血酸反应的两类速率常数，一类较快，范围为(9 - 60)×10⁹ M⁻¹ s⁻¹，另一类较慢，范围为(0.5 - 2)×10⁸ M⁻¹ s⁻¹。这些结果表明，只有在少数几种抗坏血酸浓度超过约2.5 mM的人体组织中，抗坏血酸才能阻止蛋白质自由基的进一步反应。
