title: Structural characterization of carcinogen-modified oligodeoxynucleotide adducts using matrix-assisted laser desorption/ionization mass spectrometry.
abstract: The aim of this study was to determine the chemical structure of in vitro 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-modified oligodeoxynucleotides (ODNs) by exonuclease digestion and matrix-assisted laser desorption/ionization mass spectrometry. A single-stranded 11-mer ODN, 5'-d(CCATCGCTACC), was reacted with N-acetoxy-PhIP, resulting in the formation of one major and eight minor PhIP-ODN adducts. A 10 min treatment of the major and one minor PhIP-ODN adduct with a 3'-exonuclease, bovine intestinal mucosa phosphodiesterase (BIMP), and a 5'-exonuclease, bovine spleen phosphodiesterase, results in inhibition of the primary exonuclease activity at deoxyguanosine (dG) producing 5'-d(CCATCG(PhIP)) and 5'-d(G(PhIP)CTACC) product ions, respectively. Post-source decay (PSD) of these enzymatic end products identifies dG as the sole modification site in two 11-mer ODN-PhIP adducts. PSD of the minor PhIP-ODN adduct digestion end product, 5'-d(CCATCG(PhIP)), also reveals that the PhIP adducted guanine moiety is in an oxidized form. Prolonged treatment of the PhIP-ODN adducts at 37 degrees C with BIMP induces a non-specific, or endonuclease, enzymatic activity culminating in the formation of deoxyguanosine 5'-monophosphate-PhIP (5'-dGMP-PhIP). The PSD fragmentation pattern of the 5'-dGMP-PhIP [M + H](+) ion of the major adduct confirms PhIP binds to the C-8 position of dG. For the minor adduct, PSD results suggest that PhIP binds to the C-8 position of an oxidized guanine, supporting the hypothesis that this adduct arises from oxidative degradation, resulting in a spirobisguanidino structure.
authors.affiliation: Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory, P.O. Box 808, California 94531, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Brown
authors.forename: Chris A
authors.initials: CA
authors.lastname: Harvey
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Turteltaub
authors.forename: Sharon J
authors.initials: SJ
authors.lastname: Shields
mesh_terms: D002273:Carcinogens / Q000494:pharmacology*; D018736:DNA Adducts / Q000737:chemistry* / Q000187:drug effects*; D007093:Imidazoles / Q000494:pharmacology; D015394:Molecular Structure; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D002273:Carcinogens; D018736:DNA Adducts; D007093:Imidazoles; D009838:Oligodeoxyribonucleotides; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine