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Role of Xanthurenic Acid 8‐ O ‐β‐ d ‐Glucoside, a Novel Fluorophore that Accumulates in the Brunescent Human Eye Lens ¶
Author(s) -
Thiagarajan Geetha,
Shirao Etsuko,
Ando Kanako,
Inoue Amane,
Balasubramanian Dorairajan
Publication year - 2002
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2002)0760368roxaod2.0.co2
Subject(s) - fluorophore , singlet oxygen , xanthurenic acid , photochemistry , chromophore , fluorescence , chemistry , covalent bond , lens (geology) , phototoxicity , reactive oxygen species , biophysics , biochemistry , oxygen , biology , optics , in vitro , amino acid , organic chemistry , tryptophan , paleontology , physics
We have been able to identify a blue fluorophore from the low‐molecular weight soluble fraction of human adult nondiabetic brunescent cataract lenses as xanthurenic acid 8‐ O ‐β‐ d ‐glucoside (XA8OG) (excitation = 338 nm and emission = 440 nm). To determine the role of this fluorophore in the lens, we have examined its photophysical and photodynamic properties. We found XA8OG to have a fluorescence quantum yield (ϕ) of 0.22 and a major emission lifetime of 12 ns. We found it to be a UVA‐region sensitizer, capable of efficiently generating singlet oxygen species but little of superoxide. We also demonstrated that XA8OG oxidizes proteins when irradiated with UVA light, causing photodynamic covalent chemical damage to proteins. Its accumulation in the aging human lens (and the attendant decrease of its precursor O ‐β‐ d ‐glucoside of 3‐hydroxykynurenine) can, thus, add to the oxidative burden on the system. XA8OG, thus, appears to be an endogenous chromophore in the lens, which can act as a cataractogenic agent.