The rates of photodestruction of tryptophan residues in human and bovine ocular lens proteins
Borkman, R.F.; Tassin, J.D.; Lerman, S.
Experimental Eye Research 32(6): 747-754
ISSN/ISBN: 0014-4835 PMID: 7250224 Accession: 006746463
The relative rates of photodestruction of tryptophan residues in .alpha.-, .beta.- and .gamma.-crystallin fractions from both human and bovine lenses were measured. The destruction of tryptophan was monitored by observing loss of tryptophan fluorescence, changes in the UV absorption spectra, and changes in the near-UV CD [circular dichroism] spectra. Photolysis experiments using monochromatic 290 nm radiation were performed on air-equilibrated and vacuum-degassed 1.0 mg/ml protein solutions at 25.degree. C. Both neutral aqueous buffer solutions and the denaturing solvents 8 M-urea and 5 M-guanidine hydrochloride were used in the photolysis studies.The observed rates of destruction of tryptophan residues in all 3 human crystallins were the same. Denaturing the human crystallin fractions with urea or guanidine hydrochloride did not significantly alter the photolysis rates. The same photolysis rates, and the same lack of effect of denaturation, were also observed for the bovine proteins. Vacuum degassing the lens protein solutions, prior to UV radiation, resulted in reduction in the photolysis rates by a factor of about 1/2.