title: Electrospray ionization ion trap multiple-stage mass spectrometric fragmentation pathways of leucine and isoleucine: an ab initio computational study.
abstract: We recently demonstrated the possibility to distinguish between leucine and isoleucine in several tryptic peptides by means of consecutive tandem mass steps (Armirotti et al. J. Am. Soc. Mass Spectrom. 2007; 18: 57), exploiting a gas-phase rearrangement of the immonium ion of Ile. In the present paper we explore the tandem mass spectrometric behaviour of the two amino acids. We propose a plausible structure for the diagnostic m/z 69 ion of Ile, that was reported for the first time in 1996 (Hulst and Kientz J. Mass. Spectrom. 1996; 31: 1188), and we explain why its formation is favoured with respect to Leu. Our conclusions are supported by ab initio quantum chemistry calcultations and isotope-labelled standards experiments.
authors.affiliation: Department of Experimental Medicine and Center of Excellence for Biomedical Research, University of Genoa, Viale Benedetto XV, 7 Genova, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Armirotti
authors.forename: Carlo
authors.initials: C
authors.lastname: Scapolla
authors.forename: Umberto
authors.initials: U
authors.lastname: Benatti
authors.forename: Gianluca
authors.initials: G
authors.lastname: Damonte
mesh_terms: D000595:Amino Acid Sequence; D003198:Computer Simulation; D007532:Isoleucine / Q000737:chemistry*; D007930:Leucine / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010449:Peptide Mapping / Q000379:methods*; D011487:Protein Conformation; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D007532:Isoleucine; D007930:Leucine