[Identification of a free non-tryptophan fluorophore in water-soluble fraction of human brunescent cataractous lens nucleus].
OBJECTIVE
We previously reported that a unique free fluorophore (Fl-Glc), presumably a beta-glucoside, is particularly abundant in human brunescent cataractous lens nuclei. Our preliminary experiments indicated that incubation of low-molecular weight (MW) fraction of non-brunescent lens nuclei causes an increase in a particular fluorophore (Fl-X). This study was undertaken to compare the Fl-Glc with the Fl-X and subsequently to identify the Fl-X.


METHODS
Experiment 1. The purified Fl-X and its beta-glucosidase digest (aglycon) were compared with the Fl-Glc and its aglycon, respectively, by high-performance liquid chromatography (HPLC). Experiment 2. i) The Fl-X and its aglycon were analysed by liquid chromatography/mass spectrometry (LC/MS). ii) Authentic xanthurenic acid was analysed by HPLC and LC/MS.


RESULTS
Experiment 1. The retention times of the Fl-X and the Fl-Glc exactly coincided. The fluorescence peaks of both disappeared after beta-glucosidase treatment. Experiment 2. i) LC/MS results suggested that the MWs of the Fl-X and its aglycon were 367 and 205, respectively. ii) HPLC and LC/MS results for xanthurenic acid (MW = 205) were exactly the same as those for the aglycon of the Fl-X.


CONCLUSIONS
The Fl-Glc and the Fl-X are identical, and the Fl-X (= Fl-Glc) is a glucoside of xanthurenic acid.
Ando
K
K
Department of Ophthalmology, Kanazawa University School of Medicine, Japan.
Shirao
E
E
Iwakuchi
Y
Y
Shirao
Y
Y
Inoue
A
A
D000368:Aged; D002386:Cataract / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D008401:Gas Chromatography-Mass Spectrometry; D005960:Glucosides / Q000032:analysis*; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry*; D014977:Xanthurenates / Q000032:analysis
D005960:Glucosides; D014977:Xanthurenates; C028330:xanthurenic acid