Formation of (bn-1 + H2O) ions by collisional activation of MALDI-formed peptide [M + H]+ ions in a QqTOF mass spectrometer.
Collisional activation of [M + H](+) parent ions from peptides of n amino acid residues may yield a rearrangement that involves loss of the C-terminal amino acid residue to produce (b(n-1) + H(2)O) daughters. We have studied this reaction by a retrospective examination of the m/z spectra of two collections of data. The first set comprised 398 peptides from coat protein digests of a number of plant viruses by various enzymes, where conditions in the tryptic digests were chosen so as to produce many missed cleavages. In this case, a large effect was observed-323 (b(n-1) + H(2)O) daughter ions (approximately 81%), including 185 (approximately 46%) "strong" decays with ratios (b(n-1) + H(2)O)/(b(n-1)) > 1. The second set comprised 1200 peptides, all from tryptic digests, which were carried out under more stringent conditions, resulting in relatively few missed cleavages. Even here, 190 (b(n-1) + H(2)O) ions (approximately 16%) were observed, including 87 (> 7%) "strong" decays, so the effect is still appreciable. The results suggest that the tendency for (b(n-1) + H(2)O) ion formation is promoted by the protonated side chain of a non-C-terminal basic amino acid residue, in the order arginine >> lysine > or = histidine, and that its (non-C-terminal) position is not critical. The results can be interpreted by a mechanism in which hydrogen bonding between the protonated side chain and the (n - 1) carbonyl oxygen facilitates loss of the C-terminal amino acid residue to give a product ion having a carboxyl group at the new C-terminus.
She
Yi-Min
YM
Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada.
Krokhin
Oleg
O
Spicer
Victor
V
Loboda
Alexandre
A
Garland
Gideon
G
Ens
Werner
W
Standing
Kenneth G
KG
Westmore
John B
JB
D000596:Amino Acids / Q000737:chemistry*; D036022:Capsid Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D007477:Ions; D012996:Solutions; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D014867:Water / Q000737:chemistry*
D000596:Amino Acids; D036022:Capsid Proteins; D007477:Ions; D012996:Solutions; D014867:Water