Hassan H M, Schrum L W
Department of Microbiology, North Carolina State University, Raleigh 27695-7615.
FEMS Microbiol Rev. 1994 Aug;14(4):315-23. doi: 10.1111/j.1574-6976.1994.tb00105.x.
Aerobic life-style offers both benefits and risks to living cells. The major risk comes from the formation of reactive oxygen intermediates (i.e. superoxide radical, O2-; hydrogen peroxide, H2O2; and hydroxyl radical, OH.) during normal oxygen metabolism. However, living cells are able to cope with oxygen toxicity by virtue of a unique set of antioxidant enzymes that scavenge O2- and H2O2, and prevent the formation OH.. Superoxide dismutases (SODs; EC 1.15.1.1) are metalloenzymes essential for aerobic survival. Escherichia coli contains two forms of this enzyme: an iron-containing enzyme (FeSOD) and a manganese-containing enzyme (MnSOD). In E. coli, MnSOD biosynthesis is under rigorous control. The enzyme is induced in response to a variety of environmental stress conditions including exposure to oxygen, redox cycling compounds such as paraquat which exacerbate the level of intracellular superoxide radicals, iron chelation (i.e. iron deprivation), and oxidants. A model for the regulation of the MnSOD has been proposed in which the MnSOD gene (sodA) is negatively regulated at the level of transcription by an iron-containing redox-sensitive repressor protein. The effect of iron-chelation most probably results in removal of the iron necessary for repressor activity. Recent studies have shown that sodA expression is regulated by three iron-dependent regulatory proteins, Fur (ferric uptake regulation), Fnr (fumarate nitrate regulation) and SoxR (superoxide regulon), and by the ArcA/ArcB (aerobic respiration control) system. The potential Fur-, Fnr- and ArcA-binding sites in the sodA promoter region have been identified by using different cis-acting regulatory mutations that caused anaerobic derepression of the gene.(ABSTRACT TRUNCATED AT 250 WORDS)
需氧生活方式对活细胞既有益处也有风险。主要风险来自于正常氧代谢过程中活性氧中间体的形成（即超氧阴离子自由基O₂⁻、过氧化氢H₂O₂和羟基自由基OH·）。然而，活细胞能够借助一组独特的抗氧化酶来应对氧毒性，这些酶可清除O₂⁻和H₂O₂，并防止OH·的形成。超氧化物歧化酶（SODs；EC 1.15.1.1）是需氧生存所必需的金属酶。大肠杆菌含有这种酶的两种形式：含铁酶（FeSOD）和含锰酶（MnSOD）。在大肠杆菌中，MnSOD的生物合成受到严格控制。该酶在多种环境应激条件下被诱导，包括暴露于氧气、百草枯等氧化还原循环化合物（会加剧细胞内超氧阴离子自由基水平）、铁螯合（即缺铁）和氧化剂。已提出一种MnSOD调控模型，其中MnSOD基因（sodA）在转录水平上受到一种含铁的氧化还原敏感阻遏蛋白的负调控。铁螯合的作用很可能导致去除阻遏活性所需的铁。最近的研究表明，sodA的表达受三种铁依赖性调节蛋白Fur（铁摄取调节）、Fnr（延胡索酸硝酸盐调节）和SoxR（超氧化物调节子）以及ArcA/ArcB（有氧呼吸控制）系统的调控。通过使用导致该基因厌氧去阻遏的不同顺式作用调节突变，已确定了sodA启动子区域中潜在的Fur -、Fnr - 和ArcA结合位点。（摘要截短于250字）
