Characterizing DNA photo-oxidation reactions bg high-resolution mass measurements with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

High-resolution mass measurements by matrix-assisted laser desorption/ioniz ation time-of-flight (MALDI-TOF) mass spectrometry. were employed to charac terize laser-induced oxidation of guanine in a small synthetic deoxyoligonu cleotide. The oligonucleotide was exposed to high-intensity UV radiation at 266 nm to produce modifications on the guanine base, The primary product s howed a +16 La mass shift relative to the original strand, whereas secondar y products showed mass shifts of +32 and +34 Ha, The mass shift of the prim ary product is consistent with an 8-oxoguanine modification. Hoc-ever, the reactivity: of the primary product with hot piperidine and other secondary oxidizing agents was different from that of a synthetic oligonucleotide con taining 7,8-dihydro-8-oxo-2'-deoxyguanine (8-oxoG), Based upon the results, a new reaction scheme involving the formation of an epoxide ring across th e C-l and C-5 positions by UV laser-induced oxidation is suggested, The res ults also illustrate the ability of MALDI to characterize chemical reactivi ty rapidly at the a low picomolar level. Copyright (C) 2000 John Wiley & So ns, Ltd.