Abstract：
Spermidine and other polyamines alleviate oxidative stress, yet excess spermidine seems toxic to Escherichia coli unless it is neutralized by SpeG, an enzyme for the spermidine N-acetyl transferase function. Thus, wild-type E. coli can tolerate applied exogenous spermidine stress, but ΔspeG strain of E. coli fails to do that. Here, using different reactive oxygen species (ROS) probes and performing electron paramagnetic resonance spectroscopy, we provide evidence that although spermidine mitigates oxidative stress by lowering overall ROS levels, excess of it simultaneously triggers the production of superoxide radicals, thereby causing toxicity in the ΔspeG strain. Furthermore, performing microarray experiment and other biochemical assays, we show that the spermidine-induced superoxide anions affected redox balance and iron homeostasis. Finally, we demonstrate that while RNA-bound spermidine inhibits iron oxidation, free spermidine interacts and oxidizes the iron to evoke superoxide radicals directly. Therefore, we propose that the spermidine-induced superoxide generation is one of the major causes of spermidine toxicity in E. coli.
摘要：
亚精胺和其他多胺缓解氧化应激，然而，过量的亚精胺似乎对大肠杆菌有毒，除非它被SpeG中和，亚精胺N-乙酰转移酶功能的酶。因此，野生型大肠杆菌能耐受外源亚精胺胁迫,但是大肠杆菌的ΔspeG菌株不能做到这一点。这里,使用不同的活性氧（ROS）探针并进行电子顺磁共振波谱，我们提供的证据表明，虽然亚精胺通过降低整体ROS水平来缓解氧化应激，过量的同时引发超氧自由基的产生，从而在ΔspeG菌株中引起毒性。此外，进行微阵列实验和其他生化测定，我们表明亚精胺诱导的超氧阴离子影响氧化还原平衡和铁稳态。最后,我们证明，虽然RNA结合的亚精胺抑制铁氧化，游离亚精胺相互作用并氧化铁，直接引起超氧自由基。因此,我们认为亚精胺诱导的超氧化物生成是大肠杆菌亚精胺毒性的主要原因之一。
