In situ enzymatic reclosure of opened imidazole rings of purines in DNA damaged by gamma-irradiation.
When aqueous solutions of DNA were treated with 10-500 grays of gamma-rays, the imidazole rings of some adenine and guanine residues underwent scission, resulting in the conversion of these purines to formamidopyrimidines. It was found that formamidopyrimidine-DNA glycosylase, known to remove imidazole-ring-opened 7-methylguanine from DNA, did not excise the radiation-induced non-alkylated formamidopyrimidines formed for adenine and guanine. The repair of these ring-opened purines was found to involve an enzymatic recyclizing of the opened imidazole ring that effects a restoration of the C-8 to N-9 bond. The enzyme, purine imidazole-ring cyclase reclosed the imidazole rings of 90% of ring-opened adenine or guanine, but did not close the opened imidazole ring of 7-methylguanine-derived formamidopyrimidine in DNA.
D000255:Adenosine Triphosphate / Q000378:metabolism; D019731:Carbon-Nitrogen Ligases; D002851:Chromatography, High Pressure Liquid; D004260:DNA Repair; D004269:DNA, Bacterial / Q000528:radiation effects; D043382:DNA-Formamidopyrimidine Glycosylase; D006147:Guanine / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D008025:Ligases / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D008970:Molecular Weight; D009699:N-Glycosyl Hydrolases / Q000378:metabolism*; D011687:Purines / Q000378:metabolism*
D004269:DNA, Bacterial; D011687:Purines; D006147:Guanine; D000255:Adenosine Triphosphate; D009699:N-Glycosyl Hydrolases; D043382:DNA-Formamidopyrimidine Glycosylase; D008025:Ligases; D019731:Carbon-Nitrogen Ligases; C044545:purine imidazole-ring cyclase; D008274:Magnesium