Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0086543 (cataract)
 29,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Conformational changes in the three crystallins alpha-, beta-, and gamma- in a singlet-oxygen generating system were investigated by fluorescence studies of tryptophan and covalently-bound sulfhydryl probe 4-[(N-iodoacetoxy)N-methyl]amino-7-nitrobenz-2-oxa-1,3-diazole (IANBD). Upon excitation at 295 nm, the tryptophan emission maxima of the crystallins were red-shifted by irradiation with visible light in the presence of the photosensitizer methylene blue. beta- crystallin showed the largest shift (4 nm) of the emission spectrum. Time course of the fluorescence changes by irradiation showed that the decrease in the tryptophan fluorescence yield occurs most rapidly for beta-crystallins, as compared to alpha- or gamma-crystallins. Fluorescence changes of IANBD-labeled crystallins show a 40% decrease in the fluorescence intensity of the sulfhydryl probe for beta-crystallin after one hour of irradiation. For alpha- and gamma-crystallin smaller decreases (7% and 15% respectively) were observed. Since all the sulfhydryl groups of beta-crystallin are known to be exposed on the surface of the protein (Andley et al, 1982, Biochemistry 21, 1853), these results suggest that the pronounced changes in conformation of beta-crystallin by singlet oxygen may be due to a rapid loss of the protein tertiary structure by oxidation of the sulfhydryl groups. These results have potential significance in understanding the age and cataract-related changes in the ocular lens in view of the fact that several key lens enzymes are associated with beta-crystallins in vivo.
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PMID:Fluorescence studies on tryptophan and sulfhydryl group changes of bovine lens crystallins in a photodynamic system. 404 65

13C-enriched acrylamide was employed to further delineate the action of this compound in preventing the cold cataract phenomenon when it is incorporated (in vitro) into young human and rabbit lenses. The extent of acrylamide incorporation, in the dark and with concurrent UV exposure, was monitored by 13C NMR spectroscopy. These studies provide further evidence that UV exposure causes permanent acrylamide photobinding within the lens. In such lenses, the gamma crystallin fraction of the soluble lens proteins is affected to the greatest extent. It appears to become aggregated and/or combined with the alpha and beta fractions resulting in an apparent loss of most of the gamma monomers. There is also an age-related effect with respect to the amount of acrylamide that can be incorporated into the lens. The decrease in acrylamide incorporation with age directly parallels the age-related decline in gamma crystallin levels.
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PMID:NMR analyses of the cold cataract. III. 13C acrylamide studies. 404 63

The three major bovine gamma-crystallin fractions (gamma-II, gamma-III and gamma-IV) are known to have closely related (80-90%) amino acid sequences and three-dimensional folding of the polypeptide backbone. Their chiroptical and emission properties, as measured by circular dichroism (CD) and fluorescence, are now shown to differ distinctly. The far-ultraviolet CD spectra indicate that all three gamma-crystallins have predominantly beta-sheet conformation (45-60%) with only subtle differences in secondary structure. The fluorescence emission maxima of gamma-II, gamma-III and gamma-IV, due to the four tryptophan residues, appear at 324, 329 and 334 nm, respectively, suggesting that tryptophan residues are buried in environments of decreasing hydrophobicity. Corresponding differences in quantum yield may be due to fluorescence quenching by neighboring sulfur-containing residues. Titratable tyrosines are maximal for gamma-III, as manifested from difference absorption spectra at alkaline pH. The near-ultraviolet CD spectra differ in position, magnitude and sign of tryptophan and tyrosine transitions. In addition, a characteristic CD maximum at 235 nm, presumably due to tyrosine-tyrosine exciton interactions, differs in magnitude for each gamma-crystallin. This study shows that the environment and interactions of the aromatic residues of the individual gamma-crystallin fractions are quite different. These variations in tertiary structure may be significant, in terms of stability of gamma-crystallins towards aggregation and denaturation, for understanding lens transparency and cataract formation in general.
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PMID:Structure and stability of gamma-crystallins. I. Spectroscopic evaluation of secondary and tertiary structure in solution. 406 74

In the bovine lens the gamma IV-crystallin fraction is a principal determinant of the phase separation and opacification temperature, Tc (Siezen et al, Proc. Natl. Acad. Sci. USA 82, 1985, 1701). We have now measured the effect on Tc of purified gamma IV-crystallin solutions produced by a variety of reagents which affect protein-protein, protein-water and water-water interactions. Ionic strengths less than physiological increase Tc dramatically, while higher ionic strength has very little effect. Calcium ion concentrations up to 8 mM produce no change in Tc. Glycerol and acrylamide both depress Tc linearly with reagent concentrations; Tc depression of gamma IV-crystallin by these compounds is quantitatively the same as for whole lens. Sulfhydryl reducing agents such as glutathione and dithiothreitol lower Tc, while hydrogen peroxide increases Tc. Changes in opacification temperature of gamma IV-crystallin produced by oxidizing and reducing agents are time-dependent and highly non-linear with reagent concentration. Our results clearly show that bovine gamma IV-crystallin is an important target protein for various reagents which are known perturbants of the opacification temperature of whole lens. The relevance of these findings to human diabetic and senile cataract formation is discussed.
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PMID:Controlled modulation of the phase separation and opacification temperature of purified bovine gamma IV-crystallin. 406 30

We have previously described an experimental model in vivo where cataract is induced by injection of the antimitotic bleomycin in the newborn rat. The first opacity of the lens appears 12--15 days after the injection of the drug concomitantly with a group of precise biochemical modifications among the soluble crystallins. These modifications are mainly the accumulation of two additional low-molecular-weight beta crystallin subunits (beta L subunits) and of several smaller alpha-crystallin polypeptides. Messenger RNA isolated from normal and cataractous lenses was assayed for translation in a cell-free wheat germ extract. Analysis of the translation products by one-dimensional and two-dimensional gel electrophoresis indicated that the messenger RNAs coding for the two beta L subunits are also present on normal lens polyribosomes. Purification and subsequent analysis by peptide mapping of the cataractous Beta L subunits suggest that they are precursor polypeptides of the normal low-molecular-weight beta-crystallins, which are no longer processed after translation and therefore accumulate in the pathological lens cell. On the other hand, in the translation of the cataractous mRNA in vitro, only the normal alpha chains are detected. These cataractous alpha-crystallins are therefore post-translational degradation products of the normal alpha polypeptides. This phenomenon seems similar to the one observed in the senescent lens. The possible involvement of these modifications in the etiology of this experimental cataract is discussed further.
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PMID:Messenger RNA for cataractous lens proteins are also present on normal lens polyribosomes. 616 9

The messenger RNA for a beta-crystallin polypeptide with a molecular size of 27 kilodaltons, first detected 5 to 10 days after birth in the normal mouse lens and the Nakano mouse cataract, was not detected in the Philly mouse cataract with translation in vitro. The heterozygous Philly lens had intermediate levels of the 27-kilodalton beta-crystallin polypeptide and exhibited delayed onset of the cataract. The deficiency of functional 27-kilodalton beta-crystallin messenger RNA is the earliest lesion reported yet for the Philly lens and points to a transcriptional or posttranscriptional developmental defect in this hereditary cataract.
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PMID:Deficiency of functional messenger RNA for a developmentally regulated beta-crystallin polypeptide in a hereditary cataract. 617 63

Human cataract lens crystallins are crosslinked and demonstrate a non-tryptophan blue fluorescence. We report here that exposure of lens crystallin to H2O2 within the concentration range reported for human aqueous humor, produces crosslinking of crystallin polypeptides within 10 minutes in the presence of the heme-undecapeptide from cytochrome c. Concomitantly, a blue fluorescence develops. These findings suggest the possibility that under some conditions hydrogen peroxide activation may play a role in cataractogenesis in vivo.
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PMID:The rapid H2O2-mediated nonphotodynamic crosslinking of lens crystallins generated by the heme-undecapeptide from cytochrome C: potential implications for cataractogenesis in man. 630 94

We have investigated the ability of Ca2+ to induce the formation of high molecular weight (HMW) proteins in the intact lens. Ca2+ cataracts were produced in rabbit lenses by culturing the lenses for either four days in medium containing 20 mM Ca2+ or for three days in medium containing 100 mM Ca2+. Lenses cultured in 20 and 100 mM Ca2+ medium became opaque after 20 hr and contained 30 and 200 times higher levels of Ca2+, respectively, than transparent lenses cultured in medium containing 1 mM Ca2+. Lenses exposed to 100 mM Mg2+ did not lose transparency. The opacification of the lenses extended to a depth of 1 mm into the cortical layer and did not involve the nucleus. No significant differences were found in the concentrations of either soluble or insoluble proteins present in freshly excised lenses and Ca2+ cataracts. Soluble HMW proteins, greater than 1.5 X 10(6) daltons, were in two- and five-fold greater amounts in the 20 and 100 mM Ca2+ cataracts, respectively, compared to controls. HMW protein present in the 100 mM Ca2+ cataract amounted to approximately 3% of the total soluble protein in the lens. The amount of Ca2+ present in the HMW fraction was 1 Ca2+ per 5 X 10(5) daltons, no higher than that present in the unaggregated crystallins. No evidence was found for covalent bonding in the aggregate. Results of polyacrylamide gel electrophoresis and double immunodiffusion indicated the presence of alpha- and beta- but not gamma-crystallin in the HMW protein.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Calcium-induced high molecular weight proteins in the intact rabbit lens. 643 38

The lens crystallins were analyzed in normal dogs and Miniature offSchnauzer dogs with congenital cataract formation. There was an increase in the relative proportions of alpha and beta L-crystallin and a decrease in the beta H and gamma-crystallin with increasing age in the noncataractous lens. These trends were advanced in the age-matched cataractous lenses. "Advanced aging" trends were also noted in various polypeptide components of beta-crystallin. Specifically, the appearance of a 29K band as well as a reversal of the 26K to 27.6K ratio occurred at an earlier age in the cataractous lens than in the clear lens. Three subunits of approximately 19K, 20K, and 21.5K were present on SDS-PAGE for alpha-crystallin from the cataractous lens as opposed to only two of 19K and 21.5K from the clear lens. However, if the protein was not heated following resolubilization in buffer containing 2% SDS and 5% 2-mercaptoethanol, only two subunits of 20K and 21.5K were evident in both clear and cataractous lenses. The electrophoretic behavior observed for both alpha and gamma-crystallins did not appear to be age related.
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PMID:Isolation and characterization of the crystallins of the normal and cataractous canine lens. 646 67

The murine mutation CatFraser causes a cataract in both the mutant heterozygote (C/+) and mutant homozygote (C/C). Our previous electrophoretic studies detected, in the lenses of both mutant genotypes, several proteins which did not appear to be present in normal lenses. Here we show, using more sensitive methods, that traces of these proteins previously characterized as abnormal are in fact present in normal lenses. Furthermore, these proteins have a primary structure very similar to that of the alpha-crystallins. We conclude that the mutation accelerates the degradation of alpha-crystallin, which in the normal lens proceeds at a very slow rate.
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PMID:Characterization of abnormal proteins in the soluble lens proteins of CatFraser mice. 646 70


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