title: Methylene blue-mediated photooxidation of 7,8-dihydro-8-oxo-2'-deoxyguanosine.
abstract: One well known product of the methylene blue-mediated photosensitization of 2'-deoxyguanosine (dG) in oxygen saturated aqueous solution is 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG). We observed that the rate of 8-oxodG photodecomposition by methylene blue-mediated photosensitization is approx. 3-times faster than for dG. The primary products of the methylene blue-mediated photosensitization of 8-oxodG are 2-amino-5-((2-deoxy-beta-D-erythro-pentofuranosyl)amino)-4H-imidazol-4-o ne (dIz), 2,2-diamino-4-((2-deoxy-beta-D-erythro-pentofuranosyl)amino)-5(2H)-oxazo lone (dZ), the 4R* and 4S* diastereoisomers of 4,8-dihydro-4-hydroxy-8-oxo-2'-deoxyguanosine (dO), and an as yet unidentified product with a molecular weight of 287 (dX). Except for the latter product, these compounds have all been identified following the methylene blue-mediated photooxidation of dG. Methylene blue-mediated photooxidation of 8-oxodG in D2O instead of H2O leads to a 4-fold increase in the rate of 8-oxodG photodecomposition while the addition of sodium azide retards the reaction, observations which imply that the reaction occurs via a type II (singlet oxygen mediated) mechanism. Like 8-oxodG, dIz and dZ are sensitive to hot piperidine and likely contribute to strand breaks observed in double stranded DNA exposed to methylene blue plus light followed by hot piperidine. Because 8-oxodG generates predominately G-->T transversions, the photooxidation of 8-oxodG to dIz, dO, and dX may explain the predominance of G-->C transversions in single-stranded M13mp2 bacteriophage DNA exposed to methylene blue plus light and then transfected into SOS-induced Escherichia coli.
authors.affiliation: Department of Radiobiology, Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: G W
authors.initials: GW
authors.lastname: Buchko
authors.forename: J R
authors.initials: JR
authors.lastname: Wagner
authors.forename: J
authors.initials: J
authors.lastname: Cadet
authors.forename: S
authors.initials: S
authors.lastname: Raoul
authors.forename: M
authors.initials: M
authors.lastname: Weinfeld
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000737:chemistry; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000737:chemistry; D006147:Guanine / Q000737:chemistry; D008751:Methylene Blue / Q000737:chemistry*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010777:Photochemistry; D013941:Thymine / Q000737:chemistry
chemical_list: D006147:Guanine; D000080242:8-Hydroxy-2'-Deoxyguanosine; D004247:DNA; D003849:Deoxyguanosine; D013941:Thymine; D008751:Methylene Blue