Tryptophan Oxidation by Singlet Molecular Oxygen [O2 (1Δg)]: Mechanistic Studies Using 18O-Labeled Hydroperoxides, Mass Spectrometry, and Light Emission Measurements

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