title: Formation of (bn-1 + H2O) ions by collisional activation of MALDI-formed peptide [M + H]+ ions in a QqTOF mass spectrometer.
abstract: Collisional activation of [M + H](+) parent ions from peptides of n amino acid residues may yield a rearrangement that involves loss of the C-terminal amino acid residue to produce (b(n-1) + H(2)O) daughters. We have studied this reaction by a retrospective examination of the m/z spectra of two collections of data. The first set comprised 398 peptides from coat protein digests of a number of plant viruses by various enzymes, where conditions in the tryptic digests were chosen so as to produce many missed cleavages. In this case, a large effect was observed-323 (b(n-1) + H(2)O) daughter ions (approximately 81%), including 185 (approximately 46%) "strong" decays with ratios (b(n-1) + H(2)O)/(b(n-1)) > 1. The second set comprised 1200 peptides, all from tryptic digests, which were carried out under more stringent conditions, resulting in relatively few missed cleavages. Even here, 190 (b(n-1) + H(2)O) ions (approximately 16%) were observed, including 87 (> 7%) "strong" decays, so the effect is still appreciable. The results suggest that the tendency for (b(n-1) + H(2)O) ion formation is promoted by the protonated side chain of a non-C-terminal basic amino acid residue, in the order arginine >> lysine > or = histidine, and that its (non-C-terminal) position is not critical. The results can be interpreted by a mechanism in which hydrogen bonding between the protonated side chain and the (n - 1) carbonyl oxygen facilitates loss of the C-terminal amino acid residue to give a product ion having a carboxyl group at the new C-terminus.
authors.affiliation: Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Yi-Min
authors.initials: YM
authors.lastname: She
authors.forename: Oleg
authors.initials: O
authors.lastname: Krokhin
authors.forename: Victor
authors.initials: V
authors.lastname: Spicer
authors.forename: Alexandre
authors.initials: A
authors.lastname: Loboda
authors.forename: Gideon
authors.initials: G
authors.lastname: Garland
authors.forename: Werner
authors.initials: W
authors.lastname: Ens
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: Standing
authors.forename: John B
authors.initials: JB
authors.lastname: Westmore
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D036022:Capsid Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D007477:Ions; D012996:Solutions; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D014867:Water / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D036022:Capsid Proteins; D007477:Ions; D012996:Solutions; D014867:Water