ISSN:
0030-493X
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Deprotonated dipeptides, on collisional activation, fragment by the characteristic process NH2CH(R1) CONHCH(R2)CO2- → NH2-C(R1)CONHCH(R2)CO2H → -NHCH(R2)CO2H + NH2C(R1)=C=O, when R1 and R2 = H or alkyl. However, when one of the constituent amino acids is either aspartic acid or glutamic acid, the standard cleavage becomes minor in comparison with fragmentation through the α-side-chain of Asp or Glu. For example, [Asp-Leu - H]- and [Leu-Asp - H]- both fragment principally by loss of water, a fragmentation not normally noted for peptides. In addition, [Leu-Asp - H]- loses CO2 and also forms HO2CCH=CHCO2-·. These fragmentations establish that Asp is the C-terminal amino acid. In contrast, isomeric Glu dipeptides, e.g. [Glu-Ala - H]- and [Ala-Glu - H]- undergo similar fragmentation, both competitively losing H2O and CO2. Both spectra also contain a product ion at m/z 128, identified as the pyroglutamate anion. Product ion and deuterium-labelling studies have been used in an attempt to elucidate the complex fragmentation mechanisms in these systems.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/oms.1210260413
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