Photoreactions of human lens monomeric crystallins.
Human lens beta s- and gamma A-crystallins exhibit very similar tryptophan fluorescence emission maxima (329 nm). gamma A isolated from infant human lenses is photo-oxidized by 300 nm irradiation and forms water-insoluble aggregates; beta s or gamma A from young human lenses form a small amount of water-soluble crosslinked species. At least part of the mechanism of photodamage by 300 nm irradiation is photogeneration of the oxidant H2O2 via the generation of O2- radical, this reaction occurs via photosensitization by the tryptophan photo-oxidation product N-formylkynurenine (N-FK) or related species. These results indicate that even though the tryptophan residues of beta s- and gamma A-crystallins are in hydrophobic (buried) microenvironments as compared to those of the alpha- and beta-crystallins, the photogeneration of N-FK is sufficient to produce O2- and H2O2.
Andley
U P
UP
Department of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston 02114.
Clark
B A
BA
D000293:Adolescent; D000328:Adult; D000375:Aging; D003459:Crystallins / Q000302:isolation & purification / Q000378:metabolism*; D005333:Fetus; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D007223:Infant; D007700:Kinetics; D007908:Lens, Crystalline / Q000254:growth & development*; D008875:Middle Aged; D008970:Molecular Weight; D010777:Photochemistry; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013481:Superoxides / Q000378:metabolism; D014364:Tryptophan
D003459:Crystallins; D013481:Superoxides; D014364:Tryptophan; D006861:Hydrogen Peroxide