Fluorescence studies on tryptophan and sulfhydryl group changes of bovine lens crystallins in a photodynamic system: Current Eye Research

Conformational changes in the three crystallins α-, β-, and γ- in a singlet-oxygen generating system were investigated by fluorescence studies of tryptophan and covalently-bound sulfhydryl probe 4-[(N-iodoacetoxy)N-methyl]amino-7-nitrobenz-2-oxa-l,3-diazole (IANBD). Upon excitation at 295 nm, the tryptophan emission maxima of the crystallins were red-shifted by irradiation with visible light in the presence of the photosensitizer methylene blue. β- crystallin showed the largest shift (A nm) of the emission spectrum. Time course of the fluorescence changes by irradiation showed that the decrease in the tryptophan fluorescence yield occurs most rapidly for β-crystallins, as compared to α- or γ-crystallins. Fluorescence changes of IANBD-labeled crystallins show a 40% decrease in the fluorescence intensity of the sulfhydryl probe for β-crystallin after one hour of irradiation. For α- and γ-crystallin smaller decreases (7% and 15% respectively) were observed. Since all the sulfhydryl groups of β-crystallin are...