title: Oxidative damage to a supercoiled DNA by water soluble peroxyl radicals characterized with DNA repair enzymes.
abstract: Earlier work (Paul, T., et al. (2000) Biochemistry 39, 4129-4135) has demonstrated that the water soluble positively charged peroxyl radical, (H(2)N)(2)(+)CC(CH(3))(2)OO(*) ((+)AOO(*)), caused direct strand scission of the Escherichia coli plasmid supercoiled DNA, pBR 322, with ca. 50% scission occurring at a (+)AOO(*)/base pair (bp) ratio of 0.2. There was no measurable direct scission with a negatively charged peroxyl ((-)BOO(*)) at (-)BOO(*)/bp = 24, nor with a neutral peroxyl (COO(*)) at COO(*)/bp = 5. Base modification (BM) of the same DNA by the same peroxyls has now been investigated using four base excision repair (BER) glycosylases. At (+)AOO(*)/bp = 0.04, there is 10% direct strand scission, and the Fpg protein recognized an additional 25% BM, while endonuclease (Endo) IV recognized an additional 20% BM and the other two BER enzymes did not give statistically significant BMs. None of the BER enzymes showed BMs in the DNA treated with -BOO(*). However, Fpg and Endo IV showed that at COO(*)/bp = 3.4 there was a BM comparable to that observed at (+)AOO(*)/bp = 0.04. Thus, COO(*) radicals are only ca. 1.2% as reactive toward the DNA's bases as (+)AOO(*). These results underline the importance of Coulombic forces in DNA reactions. It is also proposed that (+)AOO(*) has a higher intrinsic reactivity in H-atom abstractions and electron transfer processes than (-)BOO(*) or COO(*) radicals.
authors.affiliation: National Research Council, Ottawa, Ontario, Canada K1A 0R6.
authors.forename: Cristina
authors.initials: C
authors.lastname: Sanchez
authors.forename: R Adam
authors.initials: RA
authors.lastname: Shane
authors.forename: Thomas
authors.initials: T
authors.lastname: Paul
authors.forename: Keith U
authors.initials: KU
authors.lastname: Ingold
mesh_terms: D000578:Amidines / Q000009:adverse effects; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects / Q000502:physiology; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004278:DNA, Superhelical / Q000187:drug effects*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006031:Glycosylation; D018384:Oxidative Stress; D012995:Solubility; D013481:Superoxides / Q000009:adverse effects* / Q000737:chemistry; D014867:Water
chemical_list: D000578:Amidines; D004278:DNA, Superhelical; D014867:Water; D013481:Superoxides; C046728:2,2'-azobis(2-amidinopropane); D045643:DNA Repair Enzymes