Characterization of alpha- and gamma-glutamyl dipeptides by negative ion collision-induced dissociation.
The low-energy CID mass spectra of the [M-H](-) ions of a variety of dipeptides containing glutamic acid have been obtained using cone-voltage collisional activation. Dipeptides with the gamma-linkage, H-Glu(Xxx-OH)-OH, are readily distinguished from those with the alpha-linkage, H-Glu-Xxx-OH, by the much more prominent elimination of H-Xxx-OH from the [M-H](-) ions of the former isomers, resulting in formation of m/z 128, presumably deprotonated pyroglutamic acid. Dipeptides with the reverse linkage, H-Xxx-Glu-OH, show distinctive fragmentation reactions of the [M-H](-) ions including enhanced elimination of CO(2) and formation of deprotonated glutamic acid. Exchange of the labile hydrogens for deuterium has shown that there is considerable interchange of C-bonded hydrogens with labile (N- and O-bonded) hydrogens prior to most fragmentation reactions. All dipeptides show loss of H(2)O from [M-H](-). MS(3) studies show that the [M-H-H(2)O](-) ion derived from H-Glu-Gly-OH has the structure of deprotonated pyroglutamylglycine while the [M-H-H(2)O](-) ions derived from H-Glu(Gly-OH)-OH and H-Gly-Glu-OH show a different fragmentation behaviour indicating distinct structures for the fragment ions.
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada. aharriso@chem.utoronto.ca
Alex G
AG
Harrison
D004151:Dipeptides / Q000032:analysis* / Q000737:chemistry; D005971:Glutamates / Q000032:analysis; D018698:Glutamic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
D004151:Dipeptides; D005971:Glutamates; C082810:gamma-glutamylglutamate; D018698:Glutamic Acid