3-hydroxykynurenine transamination leads to the formation of the fluorescent substances in human lenses.
The levels of alanine, aspartate and glutamine transaminase increase considerably in some diseases. We measured the activity of these enzymes and of the transaminase of 3-hydroxykynurenine, an aminoacid, which acts as a UV lens filter. Alanine and glutamine transaminases (carboxypeptidase) were not detected in normal and cataractous human lenses, and aspartate transaminase was found only in the cortex of normal lenses. 3-hydroxykynurenine transaminase was not found in lenses from persons below thirty years of age, but was found in lenses at about fifty years of age, and in cataractous lenses. Transamination of 3-hydroxykynurenine leads to the formation of xanthurenic acid and its derivatives. These substances appear to be responsible for the increase of lens fluorescence during cataract development.
Malina
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HZ
Experimental Ophthalmology Laboratory, Swiss Institute for Experimental Research on Cancer, Lausanne, Switzerland.
Martin
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XD
D000328:Adult; D000410:Alanine Transaminase / Q000378:metabolism*; D001219:Aspartate Aminotransferases / Q000378:metabolism*; D002386:Cataract / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D006801:Humans; D007737:Kynurenine / Q000031:analogs & derivatives* / Q000378:metabolism; D007908:Lens, Crystalline / Q000201:enzymology*; D008190:Lyases; D008875:Middle Aged; D013050:Spectrometry, Fluorescence; D016339:Spectrometry, Mass, Fast Atom Bombardment; D000637:Transaminases / Q000378:metabolism; D014977:Xanthurenates / Q000378:metabolism*; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D014977:Xanthurenates; C005045:3-hydroxykynurenine; D007737:Kynurenine; C028330:xanthurenic acid; D005723:gamma-Glutamyltransferase; D000637:Transaminases; D001219:Aspartate Aminotransferases; D000410:Alanine Transaminase; C427605:glutamine - phenylpyruvate transaminase; C021481:kynurenine-oxoglutarate transaminase; D008190:Lyases