Department of Radiation Biology, Environmental Radiation Research Group, Korea Atomic Energy Research Institute, P.O. Box 105, Yusong, Taejon 305-600, South Korea.
Environ Toxicol Pharmacol. 2002 Jan;11(1):9-14. doi: 10.1016/s1382-6689(01)00093-x.
Reactive oxygen species including hydrogen peroxide (H(2)O(2)) and hydroxyl radical (OH) can be generated by ionizing radiation and has the potential to induce diseases. We provide the evidence that NAD-dependent malate dehydrogenase (MDH) is involved in the antioxidant role in preventing H(2)O(2) or γ-radiation-induced damage in Escherichia coli through the action of oxaloacetate. The E. colimdh mutant strain defective in MDH activity was more sensitive to H(2)O(2) or γ-radiation than was the wild type strain, when challenged in the exponential growth phase. The mdh mutant cells pretreated with oxaloacetate (2.5 mM), a product of NAD-dependent MDH activity, prior to H(2)O(2) treatment or γ-irradiation are resistant to H(2)O(2) or γ-radiation-induced damage, so cell survivability is restored to similar levels with the wild type. The SOS induction of umu'-'lacZ fusion gene by H(2)O(2) is significantly repressed by pretreatment of oxaloacetate in a dose-dependent way. These results indicate that oxaloacetate effectively protects E. coli cells against damage caused by oxidative stress. Oxaloacetate strongly prevented the DNA strand breaks by OH in a metal-catalyzed oxidation (MCO) system that generated H(2)O(2) as a mediator. By contrast, the prevention of DNA damage by oxaloacetate in an γ-irradiation system that directly generates OH from H(2)O in vitro was far less than that in an MCO system. Our results demonstrated that oxaloacetate, metabolite of NAD-dependent MDH action, plays a role as an antioxidant, possibly by scavenging H(2)O(2).
活性氧包括过氧化氢 (H2O2) 和羟基自由基 (OH)，可由电离辐射产生，并有可能诱发疾病。我们提供的证据表明，NAD 依赖性苹果酸脱氢酶 (MDH) 通过草酰乙酸的作用参与抗氧化作用，防止大肠杆菌中 H2O2 或 γ 辐射诱导的损伤。在指数生长期受到挑战时，缺乏 MDH 活性的大肠杆菌 mDH 突变株比野生型菌株对 H2O2 或 γ 辐射更敏感。用 NAD 依赖性 MDH 活性产物草酰乙酸（2.5 mM）预处理 mdh 突变细胞，然后用 H2O2 处理或 γ 辐照，可抵抗 H2O2 或 γ 辐射诱导的损伤，因此细胞存活率恢复到与野生型相似的水平。H2O2 诱导的 umu'-'lacZ 融合基因的 SOS 诱导，通过草酰乙酸预处理，以剂量依赖的方式被显著抑制。这些结果表明，草酰乙酸可有效保护大肠杆菌细胞免受氧化应激引起的损伤。草酰乙酸在金属催化氧化 (MCO) 系统中强烈防止由 OH 引起的 DNA 链断裂，该系统产生 H2O2 作为介质。相比之下，在体外直接从 H2O 生成 OH 的 γ 辐射系统中，草酰乙酸对 DNA 损伤的预防作用远小于 MCO 系统。我们的结果表明，NAD 依赖性 MDH 作用的代谢物草酰乙酸作为抗氧化剂发挥作用，可能通过清除 H2O2 来实现。
