title: Methylating peptides to prevent adduct ion formation also directs cleavage in collision-induced dissociation mass spectrometry.
abstract: We investigated the effect of N-terminal amino group and carboxyl group methylation on peptide analysis by electrospray mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). Permethylation of the N-terminal amino group and the carboxyl groups can reduce metal ion adducts but does not enhance sensitivity in electrospray as previously observed for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. N-terminal trimethylated peptides exhibit collision-induced dissociation (CID) tandem mass spectra that differ from their unmodified analogs; the results support the mobile proton hypothesis of peptide fragmentation. A permanent positive charge at the N-terminus leads to competition between permanent-charge directed processes and loss of the N-terminal trimethyl amino group. Carboxyl methylation has no effect on fragmentation behavior other than to shift the mass of fragments containing methylated carboxyl groups. Comparison of regular and tandem mass spectra of different methylated peptides allowed probing the location of incomplete methylation, the proton displaced by alkali metal ions and the purity of a mass-selected methylated peptide ion.
authors.affiliation: Chemistry Department, University of Ottawa, 10 Marie Curie, Ottawa, Canada K1N 6N5.
authors.forename: Clement
authors.initials: C
authors.lastname: Poon
authors.forename: Harvey
authors.initials: H
authors.lastname: Kaplan
authors.forename: Paul M
authors.initials: PM
authors.lastname: Mayer
mesh_terms: D000595:Amino Acid Sequence; D007477:Ions / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*; D008670:Metals / Q000737:chemistry; D008745:Methylation; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry*; D012680:Sensitivity and Specificity
chemical_list: D007477:Ions; D008670:Metals; D010455:Peptides