[Putrescine as a oxidative stress protecting factor in Escherichia coli].

The level of expression of oxyR, the gene that protects Escherichia coli against oxidative stress, was enhanced by physiological concentrations of the biogenic amine putrescine. This level was directly proportional to the degree of negative DNA supercoiling. 1,4-Diamino-2-butanone (DAB), a specific inhibitor of ornithine decarboxylase, the key enzyme of polyamine synthesis, produced an inhibitory effect on the level of oxyR expression under oxidative stress, which was relieved by the addition of putrescine. The direct relationship between putrescine concentration and the degree of negative DNA supercoiling suggests that the mechanism of action of putrescine as the modulator of oxyR transcription activity is based on both its direct influence on the gene expression level and its indirect effect mediated by topological DNA changes. Putrescine was shown to produce a protective effect if the DNA is damaged by reactive oxygen species.