Deamidation as a consequence of beta-elimination of phosphopeptides.

Beta-elimination procedures often precede mass spectrometric analyses of phosphorylated peptides. Unfortunately, the commonly employed reaction conditions facilitate the deamidation of amide-containing residues. In addition to being 1 Da heavier than their amide counterparts, the newly created acidic residues greatly influence peptide tandem mass spectra. The effects of deamidation are investigated for five different amide-containing synthetic peptides exposed to beta-elimination conditions. MALDI-generated ions are analyzed with a tandem TOF mass analyzer. Methodologies for estimating the degree of deamidation from peptide mass spectra are presented, the influence that adjacent residues exert on the rate of deamidation is catalogued, and the impact that deamidation can have on peptide tandem mass spectra is demonstrated. The complications this side reaction can cause for automated data interpretation are also noted.