title: Cα-C bond cleavage of the peptide backbone in MALDI in-source decay using salicylic acid derivative matrices.
abstract: The use of 5-formylsalicylic acid (5-FSA) and 5-nitrosalicylic acid (5-NSA) as novel matrices for in-source decay (ISD) of peptides in matrix-assisted laser desorption/ionization (MALDI) is described. The use of 5-FSA and 5-NSA generated a- and x-series ions accompanied by oxidized peptides [M - 2 H + H](+). The preferential formation of a- and x-series ions was found to be dependent on the hydrogen-accepting ability of matrix. The hydrogen-accepting ability estimated from the ratio of signal intensity of oxidized product [M - 2 H + H](+) to that of non-oxidized protonated molecule [M + H](+) of peptide was of the order 5-NSA > 5-FSA > 5-aminosalicylic acid (5-ASA) ≒ 2,5-dihydroxyl benzoic acid (2,5-DHB) ≒ 0. The results suggest that the hydrogen transfer reaction from peptide to 5-FSA and 5-NSA occurs during the MALDI-ISD processes. The hydrogen abstraction from peptides results in the formation of oxidized peptides containing a radical site on the amide nitrogen with subsequent radical-induced cleavage at the Cα-C bond, leading to the formation of a- and x-series ions. The most significant feature of MALDI-ISD with 5-FSA and 5-NSA is the specific cleavage of the Cα-C bond of the peptide backbone without degradation of side-chain and post-translational modifications (PTM). The matrix provides a useful complementary method to conventional MALDI-ISD for amino acid sequencing and site localization of PTMs in peptides.
authors.affiliation: Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Asakawa
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Takayama
mesh_terms: D000595:Amino Acid Sequence; D005841:Gentisates / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry*; D012459:Salicylates / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D005841:Gentisates; D007477:Ions; D010455:Peptides; D012459:Salicylates; C071881:5-nitroso-salicylate; C075234:5-fluorosalicylic acid; D006859:Hydrogen