title: Formation of [b(n) + 17 + Ag]+ product ions from Ag+ cationized native and acetylated peptides.
abstract: 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 alpha-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 alpha-carbon of the amino acid to the N-terminal side of the cleavage site.
authors.affiliation: Department of Chemistry, Wichita State University, Wichita, KS 67260-0051, USA.
authors.forename: V
authors.initials: V
authors.lastname: Anbalagan
authors.forename: B A
authors.initials: BA
authors.lastname: Perera
authors.forename: A T M
authors.initials: AT
authors.lastname: Silva
authors.forename: A L
authors.initials: AL
authors.lastname: Gallardo
authors.forename: M
authors.initials: M
authors.lastname: Barber
authors.forename: J M
authors.initials: JM
authors.lastname: Barr
authors.forename: S M
authors.initials: SM
authors.lastname: Terkarli
authors.forename: E R
authors.initials: ER
authors.lastname: Talaty
authors.forename: M J
authors.initials: MJ
authors.lastname: Van Stipdonk