Scott M D, Meshnick S R, Eaton J W
Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis 55455.
J Biol Chem. 1989 Feb 15;264(5):2498-501.
Although increased superoxide dismutase (SOD) activity is often associated with enhanced resistance of cells and organisms to oxidant challenges, few direct tests of the antioxidant importance of this enzyme have been carried out. To assess the importance of SOD in defending against gamma-radiation, we employed Escherichia coli with deficient, normal, and super-normal enzyme activities. Surprisingly, the radiation sensitivity of E. coli actually increases as bacterial SOD activity increases. Elevated intracellular SOD activity sensitizes E. coli to radiation-induced mortality, whereas SOD-deficient bacteria show normal or decreased radiosensitivity. Toxic effects of activated oxygen species are involved in this phenomenon; bacterial SOD activity has no effect on radiation sensitivity under anaerobic conditions or on the lethality of other, non-oxygen-dependent, toxins such as ultraviolet radiation.
尽管超氧化物歧化酶（SOD）活性增加通常与细胞和生物体对氧化剂挑战的抵抗力增强有关，但对这种酶的抗氧化重要性进行的直接测试却很少。为了评估SOD在抵御γ辐射中的重要性，我们使用了具有缺陷、正常和超正常酶活性的大肠杆菌。令人惊讶的是，随着细菌SOD活性的增加，大肠杆菌的辐射敏感性实际上会增加。细胞内SOD活性升高会使大肠杆菌对辐射诱导的死亡敏感，而缺乏SOD的细菌则表现出正常或降低的放射敏感性。活性氧的毒性作用参与了这一现象；细菌SOD活性在厌氧条件下对辐射敏感性没有影响，对其他非氧依赖性毒素（如紫外线）的致死性也没有影响。
