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Differentiating α‐ and β‐aspartic acids by electrospray ionization and low‐energy tandem mass spectrometry
Author(s) -
González Luis Javier,
Shimizu Takahiko,
Satomi Yoshinori,
Betancourt Lazaro,
Besada Vladimir,
Padrón Gabriel,
Orlando Ron,
Shirasawa Takuji,
Shimonishi Yasutsugu,
Takao Toshifumi
Publication year - 2000
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/1097-0231(20001130)14:22<2092::aid-rcm137>3.0.co;2-v
Subject(s) - chemistry , aspartic acid , tandem mass spectrometry , electrospray ionization , protonation , mass spectrometry , fragmentation (computing) , ion , electrospray , peptide , amino acid , collision induced dissociation , mass spectrum , dissociation (chemistry) , stereochemistry , chromatography , organic chemistry , biochemistry , computer science , operating system
Spectra obtained by low‐energy electrospray ionization tandem mass spectrometry (ESI‐MS/MS) of 34 peptides containing aspartic acids at position n were studied and unambiguously differentiated. β‐Aspartic acid yields an internal rearrangement similar to that of the C‐terminal rearrangements of protonated and cationized peptides. As a result of this rearrangement, two different ions containing the N‐ and the C‐terminal ends of the original peptide are formed, namely, the b n − 1 + H 2 O and y″ ℓ − n + 1 − 46 ions, respectively, where ℓ is the number of amino acid residues in the peptide. The structure suggested for the y″ ℓ − n + 1 − 46 ion is identical to that proposed for the v n ions observed upon high‐energy collision‐induced dissociation (CID) experiments. The intensity of these ions in the low‐energy MS/MS spectra is greatly influenced by the presence and position of basic amino acids within the sequences. Peptides with a basic amino acid residue at position n − 1 with respect to the β‐aspartic acid yield very intense b n −1 + H 2 O ions, while the y″ ℓ − n + 1 − 46 ion was observed mostly in tryptic peptides. Comparison between the high‐ and low‐energy MS/MS spectra of several isopeptides suggests that a metastable fragmentation process is the main contributor to this rearrangement, whereas for long peptides (40 AA) CID plays a more important role. We also found that α‐aspartic acid containing peptides yield the normal immonium ion at 88 Da, while peptides containing β‐aspartic acid yield an ion at m/z 70, and a mechanism to explain this phenomenon is proposed. Derivatizing isopeptides to form quaternary amines, and performing MS/MS on the sodium adducts of isopeptides, both improve the relative intensity of the b n + 1 + H 2 O ions. Based on the above findings, it was possible to determine the isomerization sites of two aged recombinant growth proteins. Copyright © 2000 John Wiley & Sons, Ltd.