title: DNA repair by thiols in air shows two radicals make a double-strand break.
abstract: Using agarose gel electrophoresis, we have measured the yields of DNA single- and double-strand breaks (SSBs and DSBs) for plasmid DNA gamma-irradiated in aerobic aqueous solution. The presence during irradiation of either of the thiols cysteamine or N-(2-thioethyl)-1,3-diaminopropane (WR-1065) resulted in a concentration-dependent decrease in the yield of SSBs and a much greater decrease in the yield of DSBs. This large differential protective effect was not produced by thioethers or an alcohol of structural similarity to the two thiols, suggesting that repair of DSB radical precursors by thiols is more efficient than for SSB precursors. These observations suggest the existence of a diradical intermediate in the formation of DSBs. The results argue against a major contribution by a single radical mechanism involving interstrand radical transfer via hydrogen abstraction by a peroxyl intermediate, since the half-life of this radical transfer reaction appears to be significantly greater than the lifetime of the intermediate.
authors.affiliation: Department of Radiology, University of California at San Diego, La Jolla 92093-0610, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Milligan
authors.forename: J Y
authors.initials: JY
authors.lastname: Ng
authors.forename: C C
authors.initials: CC
authors.lastname: Wu
authors.forename: J A
authors.initials: JA
authors.lastname: Aguilera
authors.forename: R C
authors.initials: RC
authors.lastname: Fahey
authors.forename: J F
authors.initials: JF
authors.lastname: Ward
mesh_terms: D003543:Cysteamine / Q000494:pharmacology; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D005609:Free Radicals; D008624:Mercaptoethylamines / Q000494:pharmacology; D009994:Osmolar Concentration; D013438:Sulfhydryl Compounds / Q000494:pharmacology*
chemical_list: D016166:Free Radical Scavengers; D005609:Free Radicals; D008624:Mercaptoethylamines; D013438:Sulfhydryl Compounds; C020174:N-(2-mercaptoethyl)-1,3-diaminopropane; D003543:Cysteamine; D004247:DNA; D004121:Dimethyl Sulfoxide