Characterization of Disulfide Connecting Patterns in Disulfide Peptide Isomers Based on Gas-Phase Ion/Radical Reactions

摘要

Peptide isomers containing two disulfide bonds reacted with CH_3OH to form [M+3H+CH_3OH]~(3+), in which one disulfide bond was cleaved. MS~2 mass spectra of [M+3H+CH_3OH]~(3+) for the three disulfide peptide isomers show significant difference, which can be used to distinguish the three isomers. However, unexpectedly MS~3 mass spectra of fragment ions after beam-type fragmentation of [M+3H+CH3OH] 3+ ions are quite similar to each other for isomer 2 and 3. In conclusion, MS~2 mass spectra of [M+3H+CH_3OH]~(3+) ions can be used to distinguish isomers, but no conclusive evidence can be drawn from MS3 of fragment ions containing three cysteine residues to assign disulfide connecting patterns.