A study of the lens crystallin's photodegradation in the presence of β-carotene

摘要

The aim of this study was to investigate in vitro the photochemical transformation of the lens crystallins in the presence of β- carotene upon exposure to UV radiation at 254, 301 and 366 nm wavelengths as a function of irradiation time. Irradiation of dia- lysed samples of these proteins from the cortical part of the eye at a wavelength of 254 nm (2.82 mW/cm~2) caused photooxidation of the aromatic residues (tryptophan, tyrosine, phenylalanine) and the crystallin solutions became turbid. The samples displayed increasing attenuance at a wavelength of 280 nm as photodamage proceeded. The fluorescence of tryptophan at 333 nm system- atically decreased and a new band between 400 and 500 nm appeared during UV C irradiation. However, irradiation with UV B at 301 nm (12 μW/cm~2) or UV A at 366 nm (13.08 μW/cm~2) wavelengths caused a negligible change in the protein structure; the protein solutions remained transparent even for up to 6 h of irradiation. We used a photostabilizer specific for singlet oxygen; it has been shown that the active species of oxygen appears to be responsible for the destabilisation of the protein structure, resulting in rapid aggregation, interpeptide cross-linking and modification of the constituent amino acids. Added β-carotene seems to prevent or reduce the degree of opacity produced in these solutions by the UV irradiation. For example, UV irradiation at 254 nm caused 81 decrease of the tryptophan fluorescence in the control samples and 73 decrease in the mixtures with β-carotene, this 8 difference can result from an interaction of the photost