Tandem mass spectrometry of model peptides modified with trans-2-hexenal, a product of lipid peroxidation

Small molecules formed during lipid peroxidation can react with the basic g roups in proteins through different mechanisms. Recently, substituted pyrid inium moieties were observed during in vitro incubations of lysine-containi ng peptides with 2-alkenals. To explore the dissociation behavior of peptid es with pyridinium-derivatized lysine residues, the peptide ions created th rough either matrix-assisted laser desorption/ionization or electrospray io nization were studied with tandem mass spectrometry. The permanently charge d pyridinium ions fragment primarily through the charge-remote processes. U nder high energy collision-induced dissociation, a number of diagnostic ion s were observed that could potentially be used to identify modified residue s in proteins. The origins of these ions were studied using deuterium excha nge and higher-order mass spectrometry experiments using an ion trap instru ment. Rational structures for these ions are proposed. (C) 1999 American So ciety for Mass Spectrometry.