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Identification of isomeric 5-hydroxytryptophan- and oxindolylalanine-containing peptides by mass spectrometry.

Authors
Type
Published Article
Journal
Organic Mass Spectrometry
1096-9888
Publisher
Wiley Blackwell (John Wiley & Sons)
Publication Date
Volume
47
Issue
4
Pages
453–459
Identifiers
DOI: 10.1002/jms.2058
PMID: 22689620
Source
Medline
License
Unknown

Abstract

Cells continuously produce reactive oxidative species that can modify all cellular components. In proteins, for example, cysteine, methionine, tryptophan (Trp), and tyrosine residues are particularly prone to oxidation. Here, we report two new approaches to distinguish two isomeric oxidation products of Trp residues, i.e. 5-hydroxytryptophan (5-HTP) and oxindolylalanine (Oia) residues, in peptides. First, 2-nitrobenzenesulfenyl chloride, known to derivatize Trp residues in position 2 of the indole ring, was used to label 5-HTP residues. The mass shift of 152.98 m/z units allowed identifying 5-HTP- besides Trp-containing peptides by mass spectrometry, whereas Oia residues were not labeled. Second, fragmentation of the Oia- and 5-HTP-derived immonium ions at m/z 175.08 produced ions characteristic for each residue that allowed their identification even in the presence of y(1) ions at m/z 175.12 derived from peptides with C-terminal arginine residues. The pseudo MS(3) spectra acquired on a quadrupole time-of-flight hybrid mass spectrometer displayed two signals at m/z 130.05 and m/z 132.05 characteristic for Oia-containing peptides and a group of six signals (m/z 103.04, 120.04, 130.04, 133.03, 146.04, and 148.04) for 5-HTP-cointaining peptides. In both cases, the relative signal intensities appeared to be independent of the sequence providing a specific fingerprint of each oxidative modification.

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