title: 32P-postlabelling analysis of isomeric 7-alkylguanine adducts of styrene oxide.
abstract: Styrene 7,8-oxide, which reacts preferentially at the N-7 position of guanine, yielded two pairs of diastereomers 7-(1'-hydroxy-2'-phenylethyl)-dGMP (the alpha-isomer) and 7-(2-hydroxy-2-phenylethyl)-dGMP (the beta-isomer) on reaction with deoxyguanosine-3'-monophosphate (3'-dGMP). The alpha- and beta-isomers were formed in the ratio 32:68. T4 polynucleotide kinase preferentially mediated labelling of diastereomers corresponding to the beta-isomer. The beta-diastereomers showed a labelling efficiency of 52%, whereas the alpha-isomers showed a labelling efficiency of 4%. Molecular modelling experiments showed intrinsic differences between the two isomers. The torsion angles of C8-N7-2'-Ar and C8-N7-2'-1' for the alpha-isomers were 149.9 degrees and -26.4 degrees, whereas the torsion angles of C-8-N7-1'-2' and N7-1'-2'-Ar for the beta-isomers were 105.3 degrees and 179.4 degrees. The consequent interatomic distance between one of the hydrogens on the alpha-carbon and the 3'-phosphate group on the sugar residue was 5.3 A in the alpha-isomer whereas the closest distance between the hydrogens attached to the alpha-carbon and 3'-phosphate group in the beta-isomer was 6.2 A. This arrangement probably leads to steric overcrowding at the 3'-phosphate group in alpha-isomers and these are less efficiently phosphorylated than beta-isomers. In in vitro styrene oxide-modified salmon testis DNA alpha- and beta-isomers of 7-alkylguanines were formed in the ratio 37:63. The recovery of two diastereomeric beta-isomers in a 32P-postlabelling assay was 14%, but one of the diastereomers was obtained in 3-fold greater yield than the second isomer.
authors.affiliation: Center for Nutrition and Toxicology, Karolinska Institute, Novum, Huddinge, Sweden.
authors.forename: R
authors.initials: R
authors.lastname: Kumar
authors.forename: P
authors.initials: P
authors.lastname: Vodicka
authors.forename: K
authors.initials: K
authors.lastname: Peltonen
authors.forename: K
authors.initials: K
authors.lastname: Hemminki
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000378:metabolism; D003848:Deoxyguanine Nucleotides / Q000378:metabolism*; D004852:Epoxy Compounds / Q000378:metabolism*; D008297:Male; D008956:Models, Chemical; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D013237:Stereoisomerism
chemical_list: D002273:Carcinogens; D003848:Deoxyguanine Nucleotides; D004852:Epoxy Compounds; D010761:Phosphorus Radioisotopes; D004247:DNA; C013690:styrene oxide