INVESTIGATIONS OF THE METASTABLE DECAY OF DNA UNDER ULTRAVIOLET MATRIX-ASSISTED-LASER-DESORPTION IONIZATION CONDITIONS WITH POST-SOURCE-DECAY ANALYSIS AND HYDROGEN/DEUTERIUM EXCHANGE/

The fragmentation of positive ions of DNA under the conditions of matr ix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) w as investigated by post-source decay (PSD) analysis and hydrogen/deute rium (H/D) exchange. Spectra of five different synthetic 4mer oligonuc leotides were recorded. As a main result the hypothesis was confirmed that for these ions all fragment ions result from processes, initiated by protonation/deuteration of a suitable base followed by a loss of t his base as a neutral or ion and further backbone cleavages. The three bases adenine, guanine, and cytosine all exhibit comparable lability for fragmentation. The spectra show evidence for an interaction of the adenine base with the phosphate backbone. Signals of fragments contai ning TT- and CT-cycloadducts were observed in the spectra. (C) 1998 Am erican Society for Mass Spectrometry.