| Summary: | 碩士 === 國立成功大學 === 化學系 === 87 === Human cataractous lens proteins at various ages have been studied by using gel filtration chromatography and electrophoresis. The results from gel filtration chromatography showed: the loss of water-soluble a-crystallin; the appearance of the low molecular weight proteins in nucleus; the inseparable b- and g-crystallins; the increase of water-insoluble proteins. The results from electrophoretic analyses showed: the formation of disulfide bond linked and non-disulfide bond linked high molecular weight aggregate (HMWA); the observation of a 9 KDa low molecular weight fragment assumed from post-translational modification of g-crystallin; the first fraction from gel filtration chromatography was found consisting of aA- and aB-crystallins; the second fraction was found consisting of a- b- and g-crystallins. Further study showed no glycoprotein was observed by using lectin overlays method.
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 I/758/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 cataracogenesis, 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 normal (clear) lens has a higher peak at 1617 cm-1, suggesting the ratio of I1617/I1604 can be used to evaluate the human lens morphology.
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