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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | You, Xiaojun Park, Sunny Imlay, James A. |
| Description | Author Affiliation: Park S ( Department of Microbiology, University of Illinois, Urbana, IL 61801, USA.); |
| Abstract | Since the discovery of catalase, it has been postulated that aerobic organisms generate enough oxidants to threaten their own fitness and, in particular, their genetic stability. An alternative is that these enzymes exist to defend the cell against more-abundant oxidants imposed by external sources. These hypotheses were tested directly through study of Hpx- (katG katE ahpCF) mutants of Escherichia coli, which lack enzymes to scavenge hydrogen peroxide (H2O2). These strains grew well in anaerobic medium but poorly when they were aerated. The Hpx- bacteria formed filaments and exhibited high rates of mutagenesis, both indicators of DNA damage. An additional recA mutation caused Hpx- cells to die rapidly upon aeration, even though the intracellular H2O2 was <1 microM. Spin-trap experiments detected substantial hydroxyl radicals, and cell-permeable iron chelators eliminated both the phenotypic defects and hydroxyl-radical formation, confirming that the Fenton reaction was responsible. An Hpx- oxyR strain exhibited even more DNA lesions than did the Hpx- mutant, indicating that the OxyR stress response induced protein(s) that suppressed DNA damage. One critical protein was Dps, an iron-sequestration protein, because Hpx- dps mutants exhibited sensitivity similar to that of the Hpx- oxyR mutant. These results reveal that aerobic E. coli generates sufficient H2O2 to create toxic levels of DNA damage. Scavenging enzymes and controls on free iron are required to avoid that fate. The rate constant of the Fenton reaction measured at physiological pH was much higher than under the acidic conditions that were used to determine the commonly cited value. |
| ISSN | 00278424 |
| e-ISSN | 10916490 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Issue Number | 26 |
| Volume Number | 102 |
| Language | English |
| Publisher | National Academy of Sciences |
| Publisher Date | 2005-06-01 |
| Publisher Place | United States |
| Access Restriction | Open |
| Subject Keyword | Catalase Genetics DNA Damage Escherichia Coli Proteins Escherichia Coli Hydrogen Peroxide Metabolism Periplasmic Proteins Peroxidases Physiology Cell Proliferation DNA Chemistry DNA-Binding Proteins Dose-Response Relationship, Drug Genetic Complementation Test Hydrogen-Ion Concentration Hydroxyl Radical Magnetics Models, Chemical Mutation Oxygen Peroxiredoxins Phenotype Plasmids Rec A Recombinases Repressor Proteins Time Factors Transcription Factors Multidisciplinary |
| Content Type | Text |
| Resource Type | Article |
| Subject | Multidisciplinary |
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