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THE EFFECTS OF NEAR‐UV RADIATION ON HUMAN LENS β‐CRYSTALLINS: PROTEIN STRUCTURAL CHANGES and THE PRODUCTION OF O 2 _ and H 2 O 2
Author(s) -
Andley Usha P.,
Clark Barbara A.
Publication year - 1989
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 - 10.1111/j.1751-1097.1989.tb04134.x
Subject(s) - crystallin , fluorescence , chemistry , irradiation , tryptophan , chromophore , absorption (acoustics) , yield (engineering) , photochemistry , crystallography , biophysics , biochemistry , amino acid , materials science , optics , biology , physics , nuclear physics , metallurgy , composite material
— β‐Crystallins (β 1 ,‐, β 2 ‐ and β 3 ‐crystallin) comprise nearly half the protein of the human lens. The effect of near‐UV radiation, which is one of the possible risk factors in cataract formation, on the p‐crystallins is investigated in this study. Protein intersubunit crosslinking, change in charge of the protein subunits to more acidic species and changes in protein tertiary structure (conformation) by 300 nm irradiation are reported. The fluorescence yield of protein tryptophan residues decreases by 300 nm irradiation. There is an increase in nontryptophan fluorescence (λ cx 340 nm, λ cm 400–600 nm), and in protein absorption at 340 nm, due to the formation of tryptophan photooxidation products. Both tryptophan and its oxidation products can be photoexcited by 300 nm irradiation and the latter are known to be good photosensitizers. The results provide evidence for the generation of H 2 0 2 in the irradiated human β‐crystallin solutions by the Type I photosensitizing action of the chromophores absorbing at 300 nm. The H 2 O 2 is generated via the intermediate production of O ‐ 2 anion; the latter spontaneously dismutates to H 2 0 2 , presumably via O ‐ 2 ‐ protein interactions. The amount of H 2 O 2 generated per absorbed photon is compared for various solutions of β 1 ,‐, β 2 ‐ and β 3 ‐crystallins from human lenses of different age.