Inhibition of nucleic acid and protein synthesis in Escherichia coli by oxidized polyamines and acrolein

Abstract

Enzymatically oxidized spermine and spermidine, which had been purified by SE-Sephadex chromatography, produced inhibition of nucleic acid and protein synthesis in Escherichia coli when incubated with the cells at low concentrations (0.25–1.0 mM). Full inhibition did not develop until approx. 12 min after addition of the oxidized polyamine. Preincubation of either of these compounds in the culture medium prior to addition of cells considerably reduced the time required for total inhibition. This result suggested that a secondary product(s) was partially, or perhaps fully, responsible for the observed inhibition. Previous work showed that oxidized polyamines are unstable because of two processes: β-elimination of acrolein, and condensation to larger oligoamines. The rate of this latter condensation process was second order or higher in oxidized polyamine concentration. Thus, the extent of condensation product formation was markedly dependent on the concentration of oxidized polyamines during preincubation. The development of inhibitory potency on preincubation, however, did not show the concentration dependence expected of a multimolecular reaction. It would therefore appear that formation of condensation products from dioxidized spermine cannot be responsible for the preincubation effect. However, this study revealed that very low levels (0.01–0.02 mM) of the other product of oxidized polyamine decomposition, acrolein, inhibited nucleic acid and protein synthesis in E. coli. In addition, a combination of acrolein at the level measured after preincubation, and oxidized polyamines produced inhibition similar to that found upon preincubation of oxidized polyamines alone. It is concluded that the inhibition of nucleic acid and protein synthesis by oxidized polyamines cannot be attributed to a direct effect of oxidized polyamines by themselves. The acrolein formed from decomposition of these compounds can, directly or indirectly, account for a major portion of this inhibition.