title: Specific cleavage at peptide backbone Cα-C and CO-N bonds during matrix-assisted laser desorption/ionization in-source decay mass spectrometry with 5-nitrosalicylic acid as the matrix.
abstract: The use of 5-nitrosalicylic acid (5-NSA) as a matrix for in-source decay (ISD) of peptides during matrix-assisted laser desorption/ionization (MALDI) is described herein. Mechanistically, the decay process is initiated by a hydrogen abstraction from a peptide backbone amide nitrogen by 5-NSA. Hydrogen abstraction results in formation of an oxidized peptide containing a radical amide nitrogen. Subsequently, the C(α)-C bond N-terminal to the peptide bond is cleaved to form an a·/x fragment pair. The C(α)-C bonds C-terminal to Gly residues were less susceptible to cleavage than were those of other residues. C(α)-C bonds N-terminal to Pro and Sar residues were not cleaved by the aforementioned mechanism; instead, after hydrogen abstraction from a Pro or Sar C(α)-H bond, the peptide bond N-terminal to the Pro was cleaved yielding b- and y-series ions. We also show that fragments produced by MALDI 5-NSA-induced ISD were formed independently of the ionization process.
authors.affiliation: Graduate School in Nanobioscience, Yokohama City University, Kanazawa-ku, Yokohama, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Asakawa
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Takayama
mesh_terms: D002244:Carbon / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D012459:Salicylates / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D007477:Ions; D010455:Peptides; D012459:Salicylates; D002244:Carbon; D006859:Hydrogen