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)

Short-term incubation of bovine alpha-crystallin with ascorbate alters the protein conformational stability. The denaturation curves with urea and guanidinium-chloride show different patterns, suggesting a deviation from a two-state mechanism owing to the presence of one or more intermediates in the unfolding of ascorbate-modified alpha-crystallin. Furthermore, the latter protein profiles are shifted to lower denaturant concentrations indicating a destabilizing action of ascorbate, which is capable of facilitating protein dissociation into subunits as demonstrated by gel filtration with 1.5 M-urea. The decrease in conformational stability cannot be ascribed to any major structural alteration, but rather to localized changes in the protein molecule. In fact, no difference between native and ascorbate-treated alpha-crystallin can be detected by amino acid analysis but perturbation of the tryptophan and tyrosine environment is indicated by alterations in intrinsic fluorescence. Furthermore, turbidity and light-scattering measurements suggest an involvement of the lysine side chains, since aggregability patterns with acetylsalicylic acid are significantly altered. The ascorbate-destabilizing effect on the conformational stability of alpha-crystallin, probably exerted through oxidative modification of amino acid residues and/or the formation of covalent adducts, provokes unfavourable steric interactions between residues along the polypeptide chains, thus favouring aggregation and insolubilization of crystallins which can lead to cataract formation, as also demonstrated by proteolytic digestion patterns which show a lower rate of degradation of the ascorbate-modified alpha-crystallin.
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PMID:Conformational stability of bovine alpha-crystallin. Evidence for a destabilizing effect of ascorbate. 141 62

In an effort to elucidate the molecular changes which take place in the human lens with the onset of nuclear cataract, the urea-insoluble protein fraction, solubilized with dithiothreitol, was digested with trypsin. Tryptic peptides separated by HPLC, were examined by both mass spectrometry and Edman degradation. A pentapeptide Gly-Glu-Tyr-Pro-Arg which is contained within the beta-crystallin sequence was isolated. This finding provides direct evidence that beta-crystallin is present in the urea-insoluble protein fraction which is known to be characteristic of human nuclear cataract lenses.
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PMID:Direct approach to identification, at the molecular level, of modified proteins in human nuclear cataractous lenses: beta-crystallin is a component of the urea-insoluble protein fraction. 147 78

For quantitative evaluation of cataract-related changes in lens proteins and lens water, the relative contents of water and SH residues and changes in the microenvironments of aromatic amino acid residues were quantitatively examined in cataract of the rat lens which had been induced by sodium selenite. Using Raman spectroscopy, results were compared with those of age-matched control lenses. The relative contents of water and SH residues decreased with increasing age in normal lenses from 3 to 8 weeks of age. In the cataractous lens, the relative water content increased constantly as compared with that of age-matched controls. The relative SH residue content continued to decline in the cataractous lenses of animals at every age. The microenvironments of tyrosine residues in cataractous lenses also changed progressively.
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PMID:Estimation of structural changes in the cataractous rat lens using Raman spectroscopy. 157 84

Raman spectroscopy shows that maturation of galactose cataract greatly increases the water signal (at 3417 cm-1) which is correlated with the inbibition of water in the lens. The maximum water: protein ratio (expressed as Raman intensity ratio I3417:I2936) occurs at the peripheral cortex (i.e. approximately 4.7), which is much higher than the ratios found in Emory cataract (approximately 0.3) and in cac-strain mouse cataract (approximately 0.5). It is demonstrated that Raman measurement of the intensity ratio I3417:I2936 is a more sensitive way to reflect increase of water in cataract, compared to water concentration (percentage of wet weight of the lens). The small decrease in the sulfhydryl profile along an equatorial diameter is attributed to the concentration decrease in glutathione. There is no spectroscopic evidence for extensive disulfide bond formation associated with galactosemic cataractogenesis in rat. There is an increase in the tyrosine I832:I858 ratio (normal 1.74; cataract 3.43), indicating a strengthening of the phenolic hydrogen bond, a change which has been found in Raman spectra of all cataracts studied. A comparison of the Raman spectra of normal lenses and mature cataracts reveals no change in conformation of the protein backbone.
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PMID:Galactose-induced cataract in rat: Raman detection of sulfhydryl decrease and water increase along an equatorial diameter. 280 22

Glucocorticoid-induced cataract lens in chick embryo was monitored by laser Raman spectroscopy. The lens opacity that appeared in chick embryo is a reversible one. Raman spectra show no significant change in the relative content of water or secondary structure of the proteins upon lens opacification. The intensity ratios of tyrosine doublet bands in Raman spectra between clear and opaque lens portions are changes. This change is reversible, and is interpreted as a protein-water phase separation that occurred during lens opacification.
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PMID:Glucocorticoid-induced cataract in chick embryo monitored by Raman spectroscopy. 291 7

A long-term system of organ culture for bovine lenses was used to investigate the effect of osmotic stress on lens opacification and crystallin loss. Lenses were pre-incubated in control medium containing L-[U-14C]tyrosine so that labelled crystallins were produced. The fate of these crystallins was studied in relation to two forms of osmotic stress. The addition of either ouabain or EGTA to the medium induced severe osmotic swelling and disturbance of the lens monovalent cation balance, but only the former treatment was followed by an increase in lens calcium. The changes due to osmotic stress were accompanied by loss of transparency and protein only in the lenses with increased calcium. Both opacification and increased calcium were found largely to be confined to the outer cortical fibres. Protein loss increased with time as lens calcium continued to increase. The protein recovered from the incubation medium was characterized by gel filtration and immunological techniques. The first protein detected was beta L-crystallin, and this formed the major part of the lost protein throughout, although alpha- and gamma-crystallins were detected at a later stage. Increased calcium also resulted in a change in the susceptibility of the crystallins to aggregation, since there was an increase in [14C]tyrosine incorporated into the lens high-molecular-weight (HM) fraction after exposure to ouabain, but not after exposure to EGTA. The relevance of these findings to human cataract is discussed.
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PMID:Calcium-induced opacification and loss of protein in the organ-cultured bovine lens. 308 64

Trypsin inhibition (reduction in benzoyl arginine p-nitroanilide hydrolysis), elastase inhibition (reduction in succinyl trialanyl p-nitroanilide hydrolysis), and chymotrypsin inhibition (reduction in acetyl tyrosine ethyl ester hydrolysis) by neutral extracts of mammalian lenses were estimated. The activities were found to be markedly elevated in human cortical cataract lenses compared to normal adult lenses (antielastase 7.21 +/- 3.90 units (mean +/- SD) in cataract compared to 1.46 +/- 0.57 in normals; antitryptic, 0.54 +/- 0.38 and 0.12 +/- 0.04; antichymotryptic, 1.03 +/- 0.61 and 0.297 +/- 0.055). Antielastase activity was distinctly higher in adult normal human lenses compared to infant lenses (0.159 +/- 0.068). Elastase- and trypsin-like activities were detected at low levels in all mammalian lenses. Chymotrypsin-like activity could not be observed in the lenses. The cataractous lenses had lower trypsin- and elastase-like activities compared to normal human lenses (elastase 1.20 +/- 0.643 in normal compared to 0.062 +/- 0.035 in cataract; trypsin, 0.367 +/- 0.154 and 0.069 +/- 0.038). The role of protease: inhibitor complexes in the expression of the individual activities and their role in cataractogenesis are discussed.
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PMID:Proteases and protease inhibitory activities in normal mammalian lenses and human cataractous lenses. 351 55

The concentration of the free aromatic amino acids tryptophan and tyrosine, the antioxidant uric acid and some unidentified compounds have been determined in the water-soluble extracts of parts from clear and nuclear-cataractous human lenses. With age (29-90 years) and cataract formation, associated with increasing nuclear pigmentation, no significant changes were observed in content of tryptophan, tyrosine and uric acid. Furthermore, these compounds did not show variation in distribution within the lens. An unidentified fluorophore, excitation and emission maxima of 345 and 425 nm, respectively, increases significantly in content with nuclear cataract formation, especially in the nucleus. Another unidentified, presumably aromatic compound shows a striking age-related decrease.
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PMID:Distribution of aromatic and fluorescent compounds within single human lenses. 365 75

Raman spectra have been measured for intact rat lens nuclei at various stages of aging in an attempt to gain further insight into age-related structural changes in the lens proteins, especially changes concerning protein sulfhydryl groups. Two Raman bands at 2579 and 2561 cm-1 were observed to be assignable to SH stretching modes of the cysteine residues. These bands have been attributed to "exposed" and "buried" sulfhydryl groups of the lens proteins, respectively, on the basis of a model compound study. The relative intensities of both SH stretching modes decreased with lens aging, and concurrently the intensity of a S-S stretching mode at 509 cm-1 due to disulfide bridges increased, suggesting that not only exposed but also buried protein sulfhydryl groups are converted to disulfide groups as a result of aging. The rate of the intensity decrease in the 2561 cm-1 band was similar to that in the 2579 cm-1 band. Therefore, it seems likely that the sulfhydryl groups in the two distinct environments are nearly equally subjected to the oxidation. Cysteine and cystine residues of the lens proteins gave their C-S stretching modes at 708 cm-1, indicating that they predominantly assume PC and/or PN conformers. The intensity ratio of a tyrosine doublet near 840 cm-1 (I832/I855) changed from approximately 0.86 to approximately 0.81 with the aging of the rat lens. This result implies that some tyrosine residues undergo a change in their hydrogen bonding environments during the course of aging. Of particular importance is that the relative intensity change of the tyrosine doublet with normal aging and that with cataract formation are in opposite directions.
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PMID:Inter- and intramolecular disulfide bond formation and related structural changes in the lens proteins. A Raman spectroscopic study in vivo of lens aging. 368 Feb 10

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


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