MASS-SPECTRAL IDENTIFICATION AND POSITIONAL MAPPING OF AFLATOXIN B-1-GUANINE ADDUCTS IN OLIGONUCLEOTIDES

The biological consequences of a carcinogen-DNA adduct are defined by the structure of the lesion and its position within the genome. Electr ospray ionization ion trap mass spectrometry (ESI-ITMS) is shown here to be a sensitive and rapid approach capable of defining both of these -parameters, Three isomeric oligonucleotides of the sequence 5'-CCGGAG GCC modified by the potent human carcinogen aflatoxin B-1 (AFB(1)) at different guanines were analyzed by ESI-ITMS. All three samples posses sed the same molecular ion confirming the presence of an intact aflato xin moiety in each oligonucleotide. In addition, each sample displayed a characteristic fragmentation pattern that permitted unambiguous ide ntification of the site of modification within the sequence. Furthermo re, an AFB(1)-modified oligonucleotide was converted under alkaline co nditions to its more stable formamidopyrimidine (FAPY) derivative. Ana lysis of this sample revealed the presence of a molecular ion correspo nding to the presence of the FAPY adduct and a distinctive fragmentati on pattern that paralleled the known chemical stability of the FAPY me tabolite. This approach should be of general use in the determination of not only the nature and site of covalent modifications, but also th e chemical stability of DNA adducts. (C) 1998 American Society for Mas s Spectrometry.