Comparing mass spectrometric characteristics of peptides and peptoids.
The collision-induced dissociation (CID) spectra of the [M+H]+ ions of a pentapeptide and the corresponding peptoid and retropeptoid have been compared. The spectra of the peptide and peptoid both exhibit B- and Y"-type sequence ions at identical m/z values. In contrast to the peptide, the [M+H]+ ion of the peptoid and all sequence ions containing an N-substituted glycine derivative corresponding to a tyrosine amino acid residue can easily lose a C7H6O molecule in a charge-remote fragmentation process. The presence of N-substituted glycine residues in a peptoid is further apparent from the presence of N-substituted immonium ions, which differ significantly in their fragmentation behaviour from the corresponding immonium ions observed in the spectra of common oligopeptides. Loss of the CH2 = NH imine molecule is the dominant fragmentation reaction in the CID spectra of all peptoid immonium ions investigated in this study. The elimination of the CH = NH2 ylide analogue from common peptide immonium ions is energetically less favourable as shown by ab initio calculations. The relative heat of formation of the CH = NH2 ylide neutral appeared to be 168 kJ mol-1 more than that of the CH2 = NH imine molecule.
Heerma
W
W
University of Utrecht, Bijvoet Center for Biomolecular Research, Netherlands.
Versluis
C
C
de Koster
C G
CG
Kruijtzer
J A
JA
Zigrovic
I
I
Liskamp
R M
RM
D000595:Amino Acid Sequence; D004743:Enkephalin, Leucine / Q000737:chemistry; D005998:Glycine / Q000031:analogs & derivatives / Q000737:chemistry; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D034444:Peptoids; D016339:Spectrometry, Mass, Fast Atom Bombardment
D009842:Oligopeptides; D034444:Peptoids; D004743:Enkephalin, Leucine; D005998:Glycine