title: Tryptophan oxidation by singlet molecular oxygen [O2(1Deltag)]: mechanistic studies using 18O-labeled hydroperoxides, mass spectrometry, and light emission measurements.
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.
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Graziella E
authors.initials: GE
authors.lastname: Ronsein
authors.forename: Mauricio C B
authors.initials: MC
authors.lastname: Oliveira
authors.forename: Sayuri
authors.initials: S
authors.lastname: Miyamoto
authors.forename: Marisa H G
authors.initials: MH
authors.lastname: Medeiros
authors.forename: Paolo
authors.initials: P
authors.lastname: Di Mascio
mesh_terms: D002851:Chromatography, High Pressure Liquid; D006861:Hydrogen Peroxide / Q000032:analysis* / Q000737:chemistry*; D007737:Kynurenine / Q000031:analogs & derivatives / Q000737:chemistry; D008163:Luminescent Measurements; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010103:Oxygen Isotopes; D010777:Photochemistry; D026082:Singlet Oxygen / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D014364:Tryptophan / Q000737:chemistry
chemical_list: D010103:Oxygen Isotopes; C007772:N'-formylkynurenine; D026082:Singlet Oxygen; D007737:Kynurenine; D014364:Tryptophan; D006861:Hydrogen Peroxide