Draczynska-Lusiak B, Brown O R
John M. Dalton Cardiovascular Research Center, Department of Veterinary Biomedical Sciences, University of Missouri, Columbia 65211.
Microbios. 1994;77(312):141-52.
Oxidant stress inhibits the growth of Escherichia coli, which is partially relieved by adding asparagine to the culture medium. Asparagine synthetase (AS), assayed using hydroxylamine as an amino donor, was decreased in a concentration-dependent manner by exposure of cultures to oxygen from near-anaerobic to hyperbaric oxygen (HBO) and by aerobic, but not by anaerobic, paraquat. The specific activity of AS was not decreased when cells were exposed to HBO without a carbon and energy source. HBO caused less AS inactivation in cells containing mutations in both superoxide dismutase (SOD) genes and producing no active SOD. Whether or not cells had catalase had no effect on HBO sensitivity of AS. Aerobic paraquat depressed AS less in cells lacking either catalase or superoxide dismutases. Cells which were decompressed following HBO poisoning had AS restored to normal activity whether or not chloramphenicol was present. These results indicate that asparagine synthetase is oxidant-sensitive; paraquat requires aerobic conditions and HBO requires energy metabolism for AS inactivation; and cells can repair oxidatively-damaged enzyme molecules. The failure of superoxide dismutase or catalase to protect AS suggests that its oxidant-inactivation in cells is not a simple effect of superoxide or hydrogen peroxide.
氧化应激会抑制大肠杆菌的生长，向培养基中添加天冬酰胺可部分缓解这种抑制作用。以羟胺作为氨基供体测定的天冬酰胺合成酶（AS），会因培养物暴露于从近厌氧到高压氧（HBO）的氧气中以及有氧百草枯（而非厌氧百草枯）而呈浓度依赖性降低。当细胞在没有碳源和能源的情况下暴露于HBO时，AS的比活性并未降低。在超氧化物歧化酶（SOD）基因均发生突变且不产生活性SOD的细胞中，HBO导致的AS失活较少。细胞是否具有过氧化氢酶对AS的HBO敏感性没有影响。在缺乏过氧化氢酶或超氧化物歧化酶的细胞中，有氧百草枯对AS的抑制作用较小。HBO中毒后减压的细胞，无论是否存在氯霉素，其AS活性均可恢复正常。这些结果表明，天冬酰胺合成酶对氧化剂敏感；百草枯需要有氧条件，而HBO需要能量代谢来使AS失活；并且细胞可以修复氧化损伤的酶分子。超氧化物歧化酶或过氧化氢酶无法保护AS，这表明其在细胞中的氧化失活并非超氧化物或过氧化氢的简单作用。
