title: Pathways for water loss from doubly protonated peptides containing serine or threonine.
abstract: The doubly-protonated peptides Ala-Ala-Xaa-Ala-Ala-Ala-Arg show extensive loss of H(2)O when Xaa = Ser or Thr. Using quasi-MS(3) techniques the fragmentation reactions of the [M + 2H - H(2)O](+2) ions have been studied in detail. For both Ser and Thr, the [M + 2H - H(2)O](+2) ions show three primary fragmentation reactions, elimination of CH(3)CH=NH, elimination of one Ala residue, and elimination of two Ala residues, in all cases forming doubly-charged products. From a study of the further fragmentation of these products, it is concluded that elimination of two Ala residues results in formation of a three-membered aziridine ring by interaction with the adjacent amide function as H(2)O is lost. The elimination of one Ala residue results in formation of a five-membered oxazoline ring through interaction with the N-terminal adjacent carbonyl function as H(2)O is lost. The elimination of CH(3)CH=NH appears to involve formation of an eight-membered ring by interaction with the remote N-terminal carbonyl function as H(2)O is lost. However, this initial structure undergoes rearrangement through interaction with the adjacent C-terminal carbonyl function prior to further fragmentation. The [MH - H(2)O](+) ion of Ala-Ala-Ser-Ala-Ala-Ala also shows elimination of CH(3)CH=NH, one Ala residue and two Ala residues.
authors: Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, M5S 3H6, Canada. aharriso@chem.utoronto.ca
authors: Alex G
authors: AG
authors: Harrison
mesh_terms: D001388:Aziridines / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D009842:Oligopeptides / Q000737:chemistry*; D011522:Protons; D012694:Serine / Q000737:chemistry*; D053719:Tandem Mass Spectrometry; D013912:Threonine / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D001388:Aziridines; D007477:Ions; D009842:Oligopeptides; D011522:Protons; D014867:Water; D013912:Threonine; D012694:Serine; C033132:aziridine