Novel rearranged ions observed for protonated peptides via metastable decomposition in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.
C-terminal rearrangement ions [b(n-1) + H2O] (where n refers to the total number of residues of peptides) are frequently observed for peptides which contain basic amino acid(s), especially arginine, at or near their N termini in low- and high-energy collision-induced dissociation or post-source decay (PSD) spectra. Here we report a novel rearrangement, associated with PSD for serine- or threonine-containing peptides that are susceptible to C-terminal rearrangement. Based on PSD analyses of serine- or threonine-containing bradykinin and its analogs, which have been ethyl-esterified or 18O labeled at their C termini, the [b(k) + H2O] (where k denotes the position adjacent to the left of the Ser/Thr residue) ion is generally thought to be formed by the transfer of the hydroxyl moiety of a serine or threonine residue to the carbonyl group of the residue to its left accompanied by the loss of the remaining C-terminal portion of the peptide. When the Ser/Thr is at or near the C terminus, the present [b(k) + H2O] ion could be formed via two pathways, i.e., the Ser/Thr-related rearrangement and the conventional C-terminal rearrangement, which has been clearly verified by 18O labeling at the C terminus. In addition, the ions which are formally designated as [y(m)b(l) + H2O], where y(m)b(l) denotes a b-type internal ion, are also briefly described.
Fang
S
S
Institute for Protein Research, Osaka University, Suita, Japan.
Takao
T
T
Satomi
Y
Y
Mo
W
W
Shimonishi
Y
Y
D001920:Bradykinin / Q000031:analogs & derivatives / Q000032:analysis; D008401:Gas Chromatography-Mass Spectrometry; D010103:Oxygen Isotopes; D010455:Peptides / Q000032:analysis*; D012694:Serine / Q000032:analysis; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013912:Threonine / Q000032:analysis
D010103:Oxygen Isotopes; D010455:Peptides; D013912:Threonine; D012694:Serine; D001920:Bradykinin