title: Collision-induced dissociation of diazirine-labeled peptide ions. Evidence for Brønsted-acid assisted elimination of nitrogen.
abstract: Gas-phase dissociations were investigated for several peptide ions containing the Gly-Leu* N-terminal motif where Leu* was a modified norleucine residue containing the photolabile diazirine ring. Collisional activation of gas-phase peptide cations resulted in facile N₂ elimination that competed with backbone dissociations. A free lysine ammonium group can act as a Brønsted acid to facilitate N₂ elimination. This dissociation was accompanied by insertion of a lysine proton in the side chain of the photoleucine residue, as established by deuterium labeling and gas-phase sequencing of the products. Electron structure calculations were used to provide structures and energies of reactants, intermediates, and transition states for Gly-Leu*-Gly-Gly-Lys amide ions that were combined with RRKM calculations of unimolecular rate constants. The calculations indicated that Brønsted acid-catalyzed eliminations were kinetically preferred over direct loss of N₂ from the diazirine ring. Mechanisms are proposed to explain the proton-initiated reactions and discuss the reaction products. The non-catalyzed diazirine ring cleavage and N₂ loss is proposed as a thermometer dissociation for peptide ion dissociations.
authors.affiliation: Department of Chemistry, University of Washington, Bagley Hall, Seattle, WA, 98195-1700, USA.
authors.forename: Aleš
authors.initials: A
authors.lastname: Marek
authors.forename: František
authors.initials: F
authors.lastname: Tureček
mesh_terms: D000465:Algorithms; D020816:Amino Acid Motifs; D002384:Catalysis; D041961:Deuterium Exchange Measurement; D003978:Diazomethane / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry; D055664:Electrochemical Techniques; D004735:Energy Transfer; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D009646:Norleucine / Q000737:chemistry; D009842:Oligopeptides / Q000737:chemistry*; D019920:Photoaffinity Labels / Q000737:chemistry*; D011487:Protein Conformation; D055550:Protein Stability; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D014835:Volatilization
chemical_list: D004151:Dipeptides; D009842:Oligopeptides; D019920:Photoaffinity Labels; D003978:Diazomethane; D009646:Norleucine; C015905:glycylleucine; D009584:Nitrogen