title: Formation of cytosine glycol and 5,6-dihydroxycytosine in deoxyribonucleic acid on treatment with osmium tetroxide.
abstract: OsO4 selectively forms thymine glycol lesions in DNA. In the past, OsO4-treated DNA has been used as a substrate in studies of DNA repair utilizing base-excision repair enzymes such as DNA glycosylases. There is, however, no information available on the chemical identity of other OsO4-induced base lesions in DNA. A complete knowledge of such DNA lesions may be of importance for repair studies. Using a methodology developed recently for characterization of oxidative base damage in DNA, we provide evidence for the formation of cytosine glycol and 5,6-dihydroxycytosine moieties, in addition to thymine glycol, in DNA on treatment with OsO4. For this purpose, samples of OsO4-treated DNA were hydrolysed with formic acid, then trimethylsilylated and analysed by capillary gas chromatography-mass spectrometry. In addition to thymine glycol, 5-hydroxyuracil (isobarbituric acid), 5-hydroxycytosine and 5,6-dihydroxyuracil (isodialuric acid or dialuric acid) were identified in OsO4-treated DNA. It is suggested that 5-hydroxyuracil was formed by formic acid-induced deamination and dehydration of cytosine glycol, which was the actual oxidation product of the cytosine moiety in DNA. 5-Hydroxycytosine obviously resulted from dehydration of cytosine glycol, and 5,6-dihydroxyuracil from deamination of 5,6-dihydroxycytosine. This scheme was supported by the presence of 5-hydroxyuracil, uracil glycol and 5,6-dihydroxyuracil in OsO4-treated cytosine. Treatment of OsO4-treated cytosine with formic acid caused the complete conversion of uracil glycol into 5-hydroxyuracil. The implications of these findings relative to studies of DNA repair are discussed.
mesh_terms: D001463:Barbiturates / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D003596:Cytosine / Q000031:analogs & derivatives* / Q000032:analysis; D004247:DNA / Q000378:metabolism*; D013058:Mass Spectrometry; D009992:Osmium / Q000494:pharmacology*; D009993:Osmium Tetroxide / Q000494:pharmacology*
chemical_list: D001463:Barbiturates; C049744:cytosine glycol; D009992:Osmium; C032211:isouramil; D003596:Cytosine; D004247:DNA; D009993:Osmium Tetroxide