Morgan Philip E, Dean Roger T, Davies Michael J
Free Radical Group, The Heart Research Institute, Camperdown, Sydney, NSW, Australia.
Free Radic Biol Med. 2004 Feb 15;36(4):484-96. doi: 10.1016/j.freeradbiomed.2003.11.021.
Reaction of certain amino acids, peptides, and proteins with singlet oxygen yields substrate-derived peroxides. Recent studies have shown that these species are formed within intact cells and can inactivate key cellular enzymes. This study examines potential mechanisms by which cells might remove or detoxify such peroxides. It is shown that catalase, horseradish peroxidase, and Cu/Zn superoxide dismutase do not react rapidly with these peroxides. Oxymyoglobin and oxyhemoglobin, but not the met (Fe3+) forms of these proteins, react with peptide but not protein, peroxides with oxidation of the heme iron. Glutathione peroxidase, in the presence of reduced glutathione (GSH) rapidly removes peptide, but not protein, peroxides, consistent with substrate size being a key factor. Protein thiols, GSH, other low-molecular-weight thiols, and the seleno-compound ebselen react, in a nonstoichiometric manner, with both peptide and protein peroxides. Cell lysate studies show that thiol consumption and peroxide removal occur in parallel; the stoichiometry of these reactions suggests that thiol groups are the major direct, or indirect, reductants for these species. Ascorbic acid and some derivatives can remove both the parent peroxides and radicals derived from them, whereas methionine and the synthetic phenolic antioxidants Probucol and BHT show little activity. These studies show that cells do not have efficient enzymatic defenses against protein peroxides, with only thiols and ascorbic acid able to remove these materials; the slow removal of these species is consistent with protein peroxides playing a role in cellular dysfunction resulting from oxidative stress.
某些氨基酸、肽和蛋白质与单线态氧反应会生成底物衍生的过氧化物。最近的研究表明，这些物质在完整细胞内形成，并且能够使关键的细胞酶失活。本研究考察了细胞可能去除此类过氧化物或使其解毒的潜在机制。结果表明，过氧化氢酶、辣根过氧化物酶和铜/锌超氧化物歧化酶与这些过氧化物反应不迅速。氧合肌红蛋白和氧合血红蛋白，而非这些蛋白质的高铁（Fe3+）形式，可与肽过氧化物而非蛋白质过氧化物反应，同时伴有血红素铁的氧化。谷胱甘肽过氧化物酶在存在还原型谷胱甘肽（GSH）的情况下能迅速去除肽过氧化物，但不能去除蛋白质过氧化物，这与底物大小是一个关键因素相符。蛋白质硫醇、GSH、其他低分子量硫醇以及硒化合物依布硒啉以非化学计量的方式与肽过氧化物和蛋白质过氧化物都发生反应。细胞裂解物研究表明，硫醇消耗和过氧化物去除是并行发生的；这些反应的化学计量表明硫醇基团是这些物质的主要直接或间接还原剂。抗坏血酸及其一些衍生物既能去除母体过氧化物，也能去除由它们衍生的自由基，而甲硫氨酸以及合成酚类抗氧化剂普罗布考和丁基羟基甲苯活性很低。这些研究表明，细胞对蛋白质过氧化物没有有效的酶防御机制，只有硫醇和抗坏血酸能够去除这些物质；这些物质的缓慢去除与蛋白质过氧化物在氧化应激导致的细胞功能障碍中发挥作用是一致的。
