Cellular defenses against superoxide and hydrogen peroxide

Annu Rev Biochem. 2008;77:755-76. doi: 10.1146/annurev.biochem.77.061606.161055.


Life evolved in an anaerobic world; therefore, fundamental enzymatic mechanisms and biochemical pathways were refined and integrated into metabolism in the absence of any selective pressure to avoid reactivity with oxygen. After photosystem II appeared, environmental oxygen levels rose very slowly. During this time, microorganisms acquired oxygen tolerance by jettisoning enzymes that use glycyl radicals and exposed low-potential iron-sulfur clusters, which can be directly poisoned by oxygen. They also developed mechanisms to defend themselves against superoxide (O(2)()) and hydrogen peroxide, partially reduced oxygen species that are generated as inadvertent by-products of aerobic metabolism. Contemporary organisms have inherited both the vulnerabilities and the defenses of these ancestral microbes. Current research seeks to identify these, and bacteria comprise an exceptionally accessible experimental system that has provided many of the answers. This manuscript reviews recent developments and identifies remaining puzzles.

Publication types

  • Research Support, N.I.H., Extramural
  • Review

MeSH terms

  • Bacterial Physiological Phenomena
  • Bacterial Proteins / chemistry
  • DNA / chemistry
  • DNA-Binding Proteins / chemistry
  • Escherichia coli Proteins / chemistry
  • Hydrogen Peroxide / chemistry
  • Hydrogen Peroxide / metabolism*
  • Hydroxyl Radical
  • Iron / chemistry
  • Models, Biological
  • Models, Chemical
  • Oxidative Stress
  • Oxygen / chemistry
  • Reactive Oxygen Species
  • Repressor Proteins / chemistry
  • Superoxides / metabolism*
  • Transcription Factors / chemistry


  • Bacterial Proteins
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • Fenton's reagent
  • Reactive Oxygen Species
  • Repressor Proteins
  • Transcription Factors
  • oxyR protein, E coli
  • peroxide repressor proteins
  • Superoxides
  • SoxR protein, Bacteria
  • Hydroxyl Radical
  • DNA
  • Hydrogen Peroxide
  • Iron
  • Oxygen