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Investigation of several unique tandem mass spectrometric fragmentation patterns of NFDEIDR, an orcokinin analog, and its N‐terminal dimethylated form
Author(s) -
Fu Qiang,
Li Lingjun
Publication year - 2006
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2337
Subject(s) - chemistry , fragmentation (computing) , ion , tandem mass spectrometry , mass spectrum , electrospray ionization , mass spectrometry , tandem , collision induced dissociation , isotopic labeling , stereochemistry , analytical chemistry (journal) , chromatography , organic chemistry , materials science , computer science , composite material , operating system
Orcokinins are a family of myotropic neuropeptides widely present in various decapod crustaceans and insect species. The majority of the orcokinins identified to date share a conserved sequence of NFDEIDR at their N‐termini. Electrospray ionization quadrupole time‐of‐flight tandem mass spectrometric (ESI‐QTOF‐MS/MS) analysis of doubly charged orcokinin precursor ions reveals the presence of a y (n − 1) + 10 peak, which is more intense than that for the y (n − 1) ion. To elucidate the identity of this novel fragment ion and understand the mechanism underlying this fragmentation, we employed a combined approach involving the use of isotopic N‐terminal dimethylation, methyl esterification, and isotope‐encoded NFDEIDR. Comparison of the fragmentation patterns of these chemically modified orcokinin analogs allowed the determination of the structure of the y (n − 1) + 10 ion as y (n − 1) + COH 2 O. The y x + COH 2 O ions, along with the y x + CO and y x + CONH 3 ions, are also present in the MS/MS spectra of NFDEIDR and several other peptides. Additionally, we report two other unusual fragmentation ions in the MS/MS spectra of N‐terminal dimethyl NFDEIDR (2+), which yields the novel fragment ions of the y (n − 1) + 38 ion and the [M+2H–59] 2+ ion. These two ion series involve the neutral loss of the asparagine side chain. The same sets of ions are also present in other peptides with dimethyl‐modified asparagines at the N‐terminus. The competition between the side‐chain loss and loss of dimethylamine is described. The loss of the side chain of N‐terminal dimethyl Asp 1 is reported as well. We also report for the first time the neutral loss of ammonia from the N‐terminal amino group of Asn 1 and the loss of CO 2 from the side chain of aspartic acid. Copyright © 2006 John Wiley & Sons, Ltd.