title: Mutagenesis by the autoxidation of iron with isolated DNA.
abstract: Oxygen free radicals are highly reactive species generated by many cellular oxidation-reduction processes. These radicals damage cellular constituents and have been causally implicated in the pathogenesis of many human diseases. We report here that oxygen free radicals generated by Fe2+ in aqueous solution are mutagenic. Aerobic incubation of luminal diameter X174 am3 (amber 3 mutation) DNA with Fe2+ results in decreased phage survival when the treated DNA is transfected into Escherichia coli spheroplasts. Transfection of the treated DNA into SOS-induced spheroplasts results in an increase in mutagenesis as great as 50-fold. Both killing and mutagenesis can be prevented by binding of Fe2+ with deferoxamine or by the addition of catalase or mannitol. These results suggest that DNA damage and mutagenesis brought about by Fe2+ are likely to occur by a Fenton-type mechanism that involves the generation of (i) hydrogen peroxide by the autoxidation of iron and (ii) hydroxyl radicals by the interaction of the hydrogen peroxide with Fe2+. DNA sequence analysis of the Fe2+-induced mutants indicates that reversion of the phage phenotype to wild type occurs largely by a transversion type of mutation involving substitution of deoxyadenosine for thymidine opposite a template deoxyadenosine. Mutagenesis is not abolished by incubation of Fe2+-treated luminal diameter X174 am3 DNA with an apurinic endonuclease and only partially abolished by incubation with alkali, suggesting that a large fraction of the mutagenesis by oxygen free radicals is not caused by formation of apurinic sites but instead involves an as-yet-to-be-defined alteration in deoxyadenosine. These findings raise the possibility that free iron localized in cellular DNA may cause mutations by the generation of oxygen free radicals.
mesh_terms: D010584:Bacteriophage phi X 174 / Q000235:genetics; D002614:Chelating Agents; D004247:DNA; D004279:DNA, Viral; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D043223:Deoxyribonuclease IV (Phage T4-Induced); D004706:Endodeoxyribonucleases / Q000494:pharmacology; D029968:Escherichia coli Proteins; D005609:Free Radicals; D007501:Iron; D009154:Mutation; D010084:Oxidation-Reduction; D010100:Oxygen; D013014:SOS Response, Genetics; D012972:Sodium Hydroxide / Q000494:pharmacology
chemical_list: D002614:Chelating Agents; D004279:DNA, Viral; D029968:Escherichia coli Proteins; D005609:Free Radicals; D012972:Sodium Hydroxide; D004247:DNA; D007501:Iron; D004706:Endodeoxyribonucleases; D043223:Deoxyribonuclease IV (Phage T4-Induced); C468972:endonuclease IV, E coli; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D010100:Oxygen