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Formation of [b n + 17 + Ag] + product ions from Ag + cationized native and acetylated peptides
Author(s) -
Anbalagan V.,
Perera B. A.,
Silva A. T. M.,
Gallardo A. L.,
Barber M.,
Barr J. M.,
Terkarli S. M.,
Talaty E. R.,
Van Stipdonk M. J.
Publication year - 2002
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.350
Subject(s) - chemistry , tripeptide , stereochemistry , ion , amino acid , crystallography , organic chemistry , biochemistry
We compared the tandem mass spectra of a range of native and acetylated Ag + cationized peptides to determine the influence of the derivatization step on the abundance of the [b n + 17 + Ag] + product ions. Using tripeptides, the smallest for which the mechanisms to generate [b 2 − 1 + Ag] + and [b 2 + 17 + Ag] + products are both operative, we found that in most cases acetylation causes an increase in the abundance of the C‐terminal rearrangement ion, [b 2 + 17 + Ag] + , relative to the rival N‐terminal rearrangement ion, [b 2 − 1 + Ag] + . The presence of a free amino group to bind to the metal ion significantly influences the relative abundances of the product ions. We propose a mechanism for the formation of the [b n + 17 + Ag] + that is based on the formation of a five‐membered oxazolidin‐5‐one and tetrahedral carbon intermediate that may collapse to a peptide upon release of CO and an imine, aided by the fact that the ring formed during C‐terminal rearrangement is both a hemiacylal and hemiaminal. We also identified an influence of amino acid sequence on the relative abundances of the [b n + 17 + Ag] + and [b n − 1 + Ag] + product ions, whereby bulky substituents located on the α‐carbon of the amino acid to the C‐terminal side of the cleavage site apparently promote the formation of the [b n + 17 + Ag] + product over [b n − 1 + Ag] + when the amino acid to the N‐terminal side of the cleavage site is glycine. The latter ion is the favored product, however, when the bulky group is positioned on the α‐carbon of the amino acid to the N‐terminal side of the cleavage site. Copyright © 2002 John Wiley & Sons, Ltd.