A NEW REARRANGEMENT REACTION OF PEPTIDE b IONS CONTAINING ACETYLATED LYSINE RESIDUE

摘要

The fragment ions at m/z 668, 569, 456, and 309 were detected in the dissociation of bn (n = 4-7) ions for KAcYAGFLVG model peptide. MS4 studies revealed that thesee fragments are correspond to the protonated YAGFLV-NH2, YAGFL-NH2, YAGF-NH2, YAG-NH2. However, these fragments were not detected in the mass spectra of bn (n = 4-7) ions derived from Ac-KYAGFLVG (N-terminal acetylated), Ac-KAcYAGFLVG (doubly acetylated), or KYAGFLV-NH2 (unmodified) sequences. We proposed that bn (n = 4-7) undergoes head-to-tail cyclization and followed by ring-opening process to place acetylated lysine residue at the C-terminus position. Afterwards, acetylated lysine residue was eliminated as a neutral without its N-terminus amine group and the protonated m/z 668, 569, 456, or 309 fragments were formed in the dissociation of b7, b6, b5, or b4 ion, respctively.