The effects of aging and photodynamic action on bovine lens proteins have been investigated by fluorescence and circular dichroism studies on low molecular weight (LMW) α-crystallin isolated from young (calf) and old (cow) lenses. The effect of aging on the microenvironment of tryptophan residues of α-crystallin was manifested as a 4 nm blue shift in the emission maximum of tryptophan, a decreased quantum yield as well as a decreased accessibility to the quencher acrylamide. The initial slopes (K(sv)) of Stern-Volmer plots of fluorescence quenching by acrylamide decreased from 2.7 M-1 for the calf to 1.3 M-1 for the cow α-crystallin, suggesting that the microenvironment of the tryptophan residues changes to a more buried one upon aging. Time course of the decrease of tryptophan fluorescence for both calf and cow α-crystallin by singlet oxygen was similar; however, the increase in fluorescence of photoproducts formed (N-FK or related species) was greatly diminished in the older protein suggesting that most of the surface tryptophans of α-crystallin are oxidized in the aging process. The results are consistent with the analysis of the near-UV circular dichroism spectrum of cow α-crystallin before and after singlet-oxygen treatment.
|Number of pages||11|
|State||Published - Jan 1 1986|