Superoxide accelerates DNA damage by elevating free-iron levels

Kay Keyer, James A. Imlay

Research output: Contribution to journalArticlepeer-review


Superoxide promotes hydroxyl-radical formation and consequent DNA damage in cells of all types. The long-standing hypothesis that it primarily does so by delivering electrons to adventitious iron on DNA was refuted by recent studies in Escherichia coli. Alternative proposals have suggested that superoxide may accelerate oxidative DNA damage by leaching iron from storage proteins or enzymic [4Fe-4S] clusters. The released iron might then deposit on the surface of the DNA, where it could catalyze the formation of DNA oxidants using other electron donors. The latter model is affirmed by the experiments described here. Whole-cell electron paramagnetic resonance demonstrated that the level of loose iron in superoxide-stressed cells greatly exceeds that of unstressed cells. Bacterial iron storage proteins were not the major source for free iron, since superoxide also increased iron levels in mutants lacking these iron storage proteins. However, overproduction of an enzyme containing a labile [4Fe-4S] cluster dramatically increased the free iron content of cells when they were growing in air. The rates of spontaneous mutagenesis and DNA damage from exogenous H2O2 increased commensurately. It is striking that both growth defects and DNA damage caused by superoxide ensue from its ability to damage a subset of iron-sulfur clusters.

Original languageEnglish (US)
Pages (from-to)13635-13640
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number24
StatePublished - Nov 26 1996


  • Fenton reaction
  • hydrogen peroxide
  • hydroxyl radical
  • oxidative stress
  • oxygen toxicity

ASJC Scopus subject areas

  • General


Dive into the research topics of 'Superoxide accelerates DNA damage by elevating free-iron levels'. Together they form a unique fingerprint.

Cite this