Formation of [b3 - 1 + cat]+ ions from metal-cationized tetrapeptides containing beta-alanine, gamma-aminobutyric acid or epsilon-aminocaproic acid residues.
The presence and position of a single beta-alanine (betaA), gamma-aminobutyric acid (gammaABu) or epsilon-aminocaproic acid (Cap) residue has been shown to have a significant influence on the formation of b(n)+ and y(n)+ product ions from a series of model, protonated peptides. In this study, we examined the effect of the same residues on the formation of analogous [b3 - 1 + cat]+ products from metal (Li+, Na+ and Ag+)-cationized peptides. The larger amino acids suppress formation of b3+ from protonated peptides with general sequence AAXG (where X = beta-alanine, gamma-aminobutyric acid or epsilon-aminocaproic acid), presumably because of the prohibitive effect of larger cyclic intermediates in the 'oxazolone' pathway. However, abundant [b3 - 1 + cat]+ products are generated from metal-cationized versions of AAXG. Using a group of deuterium-labeled and exchanged peptides, we found that formation of [b3 - 1 + cat]+ involves transfer of either amide or alpha-carbon position H atoms, and the tendency to transfer the atom from the alpha-carbon position increases with the size of the amino acid in position X. To account for the transfer of the H atom, a mechanism involving formation of a ketene product as [b3 - 1 + cat]+ is proposed.
Osburn
Sandra M
SM
Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, KS 67260-0051, USA.
Ochola
Sila O
SO
Talaty
Erach R
ER
Van Stipdonk
Michael J
MJ
D015119:Aminocaproic Acid / Q000737:chemistry*; D002412:Cations; D007477:Ions; D008670:Metals / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D015091:beta-Alanine / Q000737:chemistry*; D005680:gamma-Aminobutyric Acid / Q000737:chemistry*
D002412:Cations; D007477:Ions; D008670:Metals; D010455:Peptides; D015091:beta-Alanine; D005680:gamma-Aminobutyric Acid; D015119:Aminocaproic Acid