Raman vibrations of the fingerprint of aromatic amino acid residues were analyzed to study the changes of cataractous lens protein in the cortex and nucleus at various ages. Tryptophan content, analyzed by the quantification of I758/I1448 ratio, shows the damage (modification) of tryptophan residue in the nucleus is caused primarily by the formation of cataracts, not by the aging process. Microenvironmental changes of tryptophan and tyrosine were analyzed by the intensity ratios of I879/I758 and I829/I853, respectively. The decrease of the ratio of I879/I758, from 0.9 to 0.6 in the nucleus and from 0.7 to 0.6 for the cortex, reveal that more buried tryptophan residues become exposed in the cortex than in the nucleus during cataractogenesis, especially for non-senile cataractous lenses. The ratio of I829/I853 is around 1.0 for both cortical and nuclear proteins at various ages, indicating some tyrosine residues have undergone a change in their hydrogen bonding environment. When compared to previous studies, we found that a normal (clear) lens has a higher peak at 1617 cm-1 than at 1604 cm-1, while a dense opaque or brunescent lens shows stronger intensity at 1604 cm-1 than at 1617 cm-1, suggesting the ratio of I1617/I1604 can be used to evaluate the human lens morphology.
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