RESUMO
The growth of Escherichia coli mutants deficient in glutathione synthesis (gshA) and in glutathione reductase (gor) was suppressed in medium of elevated osmolarity. A mutant in gamma-glutamyl transpeptidase (ggt) displayed better ability for osmoadaptation than the parental strain. The unfavorable effect of the gsh mutation on osmoadaptation of growing E. coli cells was more pronounced at low concentrations of K+ in the medium. An increase in osmolarity caused an increase in the intracellular content of glutathione. Changes in the extracellular glutathione level were biphasic: the glutathione level rapidly decreased during the first stage of the response and increased during the second stage. The changes in glutathione levels suggest that under hyperosmotic shock the glutathione transport from the medium into the cell can contribute to the intracellular glutathione accumulation. Changes in the level of intracellular K+ were similarly biphasic: a rapid increase in the K+ level during the first stage of the response to hyperosmotic shock changed to a gradual decrease during the second stage. In mutant gshA cells adapted to osmotic shock, the intracellular K+ level was markedly higher than in the parental strain cells. The possible role of glutathione in the response of E. coli to osmotic shock is discussed.
Assuntos
Enzimas/metabolismo , Escherichia coli/fisiologia , Glutationa/fisiologia , Divisão Celular , Enzimas/genética , Escherichia coli/efeitos dos fármacos , Glutationa Redutase/genética , Glutationa Redutase/metabolismo , Mutação , Concentração Osmolar , Pressão Osmótica , Oxirredução , Potássio/metabolismo , Cloreto de Sódio/farmacologia , gama-Glutamiltransferase/genética , gama-Glutamiltransferase/metabolismoRESUMO
Sensitivity to various oxidants was determined for Escherichia coli strains JTG10 and 821 deficient in biosynthesis of glutathione (gsh-) and their common parental strain AB1157 (gsh+). The three strains showed identical sensitivity to H2O2. E. coli 821 was more resistant than AB1157 and JTG10 to menadione, cumene hydroperoxide, and N-ethylmaleimide. This resistance was not related to the gsh mutation because the other gsh- mutant and the parental strain showed similar sensitivity to these oxidants. The measured activities of NADPH:menadione diaphorase and glucose-6-phosphate dehydrogenase and the extracellular level of menadione suggested that the enhanced resistance of E. coli 821 to menadione might be due to decreased diaphorase activity, but not to a lowered rate of menadione uptake.
