Collision-Induced Dissociations of Deprotonated Dipeptide Methyl Esters Containing Serine or Threonine

Abstract

The collision-induced mass spectra (MS/MS) of (M - H)- ions derived from dipeptide methyl esters containing serine or threonine lack the characteristic backbone cleavage of the underivatized peptides (which provide primary sequencing data). Instead, competitive fragmentation occurs through the ester and α-side chain functions. For example, Ser methyl esters lose both CH2O (from the side chain) and MeOH ( MeO comes from the methyl ester). Isomeric dipeptides may be differentiated by competitive fragmentations; for example [ Gly Ser( OMe )-H]- fragments first by loss of CH2O, while [Ser Gly ( OMe )-H]-, in contrast, shows initial elimination of MeOH. The structures of the product ions in these spectra have been probed by deuterium labelling and MS/MS/MS studies.

The Negative Ion Mass Spectra of [M-H]− Ions Derived From Caeridin and Dynastin Peptides. Internal Backbone Cleavages Directed Through Asp and Asn Residues

“…The B and (Y + 2) backbone cleavages 8 of the MH + ions often provide the full amino acid sequence of the caeridin and dynastin peptides; in other cases at least 80% of the sequence can be so determined. [1][2][3][4][5] During the last decade, we have studied the fragmentations of the [M-H] -ions of small underivatized peptides (for reviews see Ref. 9).…”

“…[1][2][3][4][5] Amongst the latter are the caeridins (from Litoria species [1][2][3] ) and the dynastins (from Limnodynastes species 4,5 ), whose molecular weights range from 850 to 1600 Da. In our structural studies [1][2][3][4][5] of these peptides, we used a combination of fast-atom bombardment (FAB) mass spectrometry, Edman degradation mass spectrometry, 6 and automated Edman sequencing 7 to determine the amino acid sequences. The B and (Y + 2) backbone cleavages 8 of the MH + ions often provide the full amino acid sequence of the caeridin and dynastin peptides; in other cases at least 80% of the sequence can be so determined.…”

A Comparison of the Effects of Amide and Acid Groups at the C-Terminus on the Collision-Induced Dissociation of Deprotonated Peptides

“…Cholecystokinin also has two aspartic acid residues in its sequence; acidic amino acid residues yield significant H 2 O loss [51,54]. In addition, serine is responsible for the production of abundant CH 2 O loss in the spectra of deprotonated SWAMVR and MLGFRSVGYA [43,53,58,90].…”

“…Their work demonstrated an unpredictable effect on the efficacy and no effect on the selectivity of the peptides studied. Krstenansky et al [22] synthesized several Cterminal analogs of hirudin (54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65) to probe the structureactivity relationship. The C-terminal amide was among the modifications studied and its presence lessened the activity of the antithrombin peptide.…”

“…The CID spectrum of YIGSR-OMe (Supplementary Figure S3) is dominated by products formed from elimination of CH 3 OH from the methyl ester functional group. There have been previous reports of CH 3 OH loss in CID of peptide methyl esters [57,58]. Laminin acid (Figure 1a) produces [c 2 -NH 3 ]…”