الفهرس 
cover EnglishOnly 14 pages are availabe for public view
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Abstract
Crystallins could be exposed to a variety of stresses throughout their lifespan leading to changes in protein assembly. Binding of sensitizers to lens proteins can readily compromise the viability of that organ by increasing the retention time of the sensitizes in the lens with a concomitant increase in the likelihood of photooxidtive damage. In this study, the interaction ofRB and HP-IX with the major lens protein ”alpha-crystallin” was investigated using spectroscopic techniques. It was demonstrated that RB was able to bind to alpha-crystallin in a condition favorably less polar environment and the hydrophobic Trp is expected to be involved in this interaction. It seems that alpha-crystallin is exposed to two different transition states upon binding with RB depending on the protein concentration. The binding constant (Kg) was quantitatively estimated by means of a spectroscopic titration technique and estimated to be of the order of 2.5 (mg/ml)”. Stern- Volmer plot demonstrated that the intrinsic fluorescence of alpha-crystallin was quenched by RB through both dynamic and static quenching. Upon visible irradiation, it was shown that the dye is exposed to photobleaching that was mainly attributed to aggregate formation. Both absorption and fluorescence emission spectra of RB bound to alpha-crystallin showed a less significant decay when compared to that of free RB. The decrease in the intrinsic fluorescence of the protein in the presence of RB was attributed to the photooxidation of Trp residues and/or change in the organized structure of the protein getting the Trp buried inside. FT-IR measurements showed that the secondary structure of alpha-crystallin is exposed to modification when complexed to RB in the dark. Light-induced photosensitized effects showed further structural modifications including an increase in unordered structure. Even though. the photoinduced structural modifications, alpha-crystallin was able to preserve its chaperone like activity in the presence of RB both in the dark and following irradiation using chaperone assay. On the contrary HP-IX sensitizer did not show an affinity towards alpha-crystallin.