title: Peptide quantitation with methyl iodide isotopic tags and mass spectrometry.
abstract: A novel method is presented for the quantitation of peptides based on their methylation by in vacuo chemical reaction with methyl iodide. Samples of two small peptides, hexaglycine and pentaalanine, were labeled with CH(3)I and CD(3)I, representing the "unknown" and "standard" respectively, and then subjected to a series of tests using mass spectrometry to ascertain the suitability of the isotopic labels for peptide quantitation. The experiments show methyl iodide to be a very quantitative label, exhibiting a linear relationship in concentration over the dynamic range of the mass spectrometer used in the analysis (up to 4 orders of magnitude) both as pure samples and in a complex mixture of peptides. The tendency of trimethylated peptides to preferentially form a(2) fragment ions in MS(2) produces a significant increase in sensitivity, especially when the mass spectrometer is used in the MRM mode. Tests were also performed to verify the stability of the label against H/D exchange and its suitability for long-term storage, showing little degradation while in solution and during subsequent chemical processing.
authors.affiliation: Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3.
authors.forename: Voislav
authors.initials: V
authors.lastname: Blagojevic
authors.forename: Nickholas
authors.initials: N
authors.lastname: Zhidkov
authors.forename: Samuel
authors.initials: S
authors.lastname: Tharmaratnam
authors.forename: Van Thong
authors.initials: VT
authors.lastname: Pham
authors.forename: Harvey
authors.initials: H
authors.lastname: Kaplan
authors.forename: Diethard K
authors.initials: DK
authors.lastname: Bohme
mesh_terms: D041961:Deuterium Exchange Measurement; D006847:Hydrocarbons, Iodinated / Q000737:chemistry*; D007553:Isotope Labeling; D008745:Methylation; D010455:Peptides / Q000032:analysis*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D006847:Hydrocarbons, Iodinated; D010455:Peptides; C014055:methyl iodide