TANDEM MASS-SPECTROMETRY OF PEPTIDES WITH N-TERMINAL GLUTAMINE - STUDIES ON A PRION PROTEIN PEPTIDE

This paper reports the unusual collision-induced fragmentation of peptides having N-terminal glutamine. One of these glutamine-containing peptides was isolated from an endo-proteinase Lys-C digest of the scrapie prion protein (PrP 27-30) with the predicted sequence QHTVTTTTK. Daughter ion mass spectra show predominant N-terminal an bn and, to a lesser extent, cn sequence ion series at 17 u less than the predicted masses. This is interpreted as arising from an ionic fragmentation that accompanies the peptide-backbone cleavage, glutamine losing ammonia to give pyroglutamic acid, a reaction that parallels the commonly observed solution-phase process. This behavior is less evident when strongly basic residues near the C-terminus cause the C-terminal fragments (xn, yn, and zn) to predominate. © 1990 American Society for Mass Spectrometry.