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Tryptophan oxidation by singlet molecular oxygen [O2(1Deltag)]: mechanistic studies using 18O-labeled hydroperoxides, mass spectrometry, and light emission measurements.

Authors
  • Ronsein, Graziella E
  • Oliveira, Mauricio C B
  • Miyamoto, Sayuri
  • Medeiros, Marisa H G
  • Di Mascio, Paolo
Type
Published Article
Journal
Chemical Research in Toxicology
Publisher
American Chemical Society
Publication Date
Jun 01, 2008
Volume
21
Issue
6
Pages
1271–1283
Identifiers
DOI: 10.1021/tx800026g
PMID: 18457429
Source
Medline
License
Unknown

Abstract

Proteins have been considered important targets for reactive oxygen species. Indeed, tryptophan (W) has been shown to be a highly susceptible amino acid to many oxidizing agents, including singlet molecular oxygen [O2(1Deltag)]. In this study, two cis- and trans-tryptophan hydroperoxide (WOOH) isomers were completely characterized by HPLC/mass spectrometry and NMR analyses as the major W-oxidation photoproducts. These photoproducts underwent thermal decay into the corresponding alcohols. Additionally, WOOHs were shown to decompose under heating or basification, leading to the formation of N-formylkynurenine (FMK). Using 18O-labeled hydroperoxides (W18O18OH), it was possible to confirm the formation of two oxygen-labeled FMK molecules derived from W18O18OH decomposition. This result demonstrates that both oxygen atoms in FMK are derived from the hydroperoxide group. In addition, these reactions are chemiluminescent (CL), indicating a dioxetane cleavage pathway. This mechanism was confirmed since the CL spectrum of the WOOH decomposition matched the FMK fluorescence spectrum, unequivocally identifying FMK as the emitting species.

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