Depurination from DNA of 7-methylguanine, 7-(2-aminoethyl)-guanine and ring-opened 7-methylguanines.
DNA was reacted with dimethyl sulphate and ethyleneimine to afford respective 7-methylguanine and 7-(2-aminoethyl)guanine derivatives. The substituted DNA was boiled in 0.1 M NaCl containing 10 mM phosphate buffer (pH 7.0), and the release of 7-alkylguanines, guanine and adenine was followed. The half-lives of depurination were 1.5 and 4.1 min for 7-(2-aminoethyl)guanine and 7-methylguanine, respectively. 7-Methylguanine was released some 60 times faster than guanine and adenine. When 7-methylguanine-containing DNA was treated in alkali to cause imidazole ring-opening, two products were liberated by boiling the DNA solution. These products were released with apparent half-lives of 69 and 34 min. These ring-opened products isomerized to each other completely within 1 h at 37 degrees C. The isomers had an identical ultraviolet spectrum and they displayed a pKa of 9.8. When silylated and analysed in gas chromatography-mass spectroscopy the two isomers had an identical molecular weight and fragmentation pattern, consistent with a structural assignment as N5-methyl-N5-formyl-2,5,6-triamino-4-oxopyrimidine. Only one of the isomers appeared to be present on DNA; the isomerization took place when the ring-opened product was released into solution.
Hemminki
K
K
Institute of Occupational Health, Helsinki, Finland.
Peltonen
K
K
Vodicka
P
P
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006147:Guanine / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure
D006147:Guanine; C008450:7-methylguanine; C060428:7-(2-aminoethyl)guanine; D004247:DNA