Tkachenko A G, Nesterova L Yu
Institute of Ecology and Genetics of Microorganisms, Ural Division of the Russian Academy of Sciences, Perm 614081, Russia.
Biochemistry (Mosc). 2003 Aug;68(8):850-6. doi: 10.1023/a:1025790729797.
Activity of enzymes of polyamine synthesis and contents of their products increased in E. coli cells in response to oxidative stress caused by addition of hydrogen peroxide to an exponentially growing culture. Putrescine and spermidine added to the culture medium in physiological concentrations significantly increased expression of genes oxyR and katG responsible for defense against oxidative stress, whereas cadaverine had no effect. The role of polyamines as modulators of the gene expression was confirmed by experiments with an inhibitor of polyamine synthesis, 1,3-diaminopropane, which decreased the level of cell polyamines and thus abolished the ability of the cell to induce oxyR expression under oxidative stress. A genetic method gave similar results: under oxidative stress mutants with disorders in polyamine synthesis displayed a significantly decreased level of induction of the oxyR and katG genes, and this level was recovered on addition of putrescine. In the presence of inhibitors of DNA-gyrase, nalidixic acid and novobiocin, the oxyR expression depended on the extent of DNA supercoiling. Putrescine decreased the inhibitory effects of nalidixic acid and novobiocin, and this confirmed its properties of a stimulator of DNA supercoiling. Resistance to rifampicin was studied to exemplify the mutation rate under oxidative stress. Putrescine decreased twofold the level of mutations and increased the number of viable cells in the culture exposed to oxidative stress.
在指数生长的大肠杆菌培养物中添加过氧化氢所引发的氧化应激反应下，大肠杆菌细胞内多胺合成酶的活性及其产物含量增加。向培养基中添加生理浓度的腐胺和亚精胺可显著增加负责抗氧化应激的oxyR和katG基因的表达，而尸胺则无此作用。用多胺合成抑制剂1,3 - 二氨基丙烷进行的实验证实了多胺作为基因表达调节剂的作用，该抑制剂降低了细胞内多胺水平，从而消除了细胞在氧化应激下诱导oxyR表达的能力。遗传学方法也得到了类似结果：在氧化应激下，多胺合成紊乱的突变体中oxyR和katG基因的诱导水平显著降低，添加腐胺后该水平得以恢复。在DNA促旋酶抑制剂萘啶酸和新生霉素存在的情况下，oxyR的表达取决于DNA超螺旋的程度。腐胺降低了萘啶酸和新生霉素的抑制作用，这证实了其作为DNA超螺旋刺激剂的特性。通过研究对利福平的抗性来例证氧化应激下的突变率。腐胺使氧化应激培养物中的突变水平降低了两倍，并增加了活细胞数量。
