Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.17 (lysozyme)
 21,489 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Guanidine hydrochloride (GdnHCl) and urea denaturations of lysozyme have been observed at various temperatures by measuring changes in fluorescence. Both transitions appear to be two state, with GdnHCl almost twice as effecitve a denaturant as urea for this protein. By plotting the denaturant concentrations at midpoint of the transition vs. the experimental temperature, it can be demonstrated that urea-denatured lysozyme does not obtain the degree of unfolding found in lysozyme denatured by GdnHCl.
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PMID:Comparison of temperature effect on the guanidine hydrochloride and urea denaturations of lysozyme. 53 98

Triclinic crystals of hen egg-white lysozyme cross-linked with glutaraldehyde have been treated with various denaturants and found to be susceptible to x-ray structure analysis even after major conformational changes in the protein. Cross-linked crystals were isomorphous with the native form, and electron density difference maps indicated the locations of intermolecular corss-links, but showed no appreciable differences in the protein conformation. Soaking of the cross-linked crystals in danaturant solutions of increasing concentrations caused corresponding increases in crystal volume and decreases in minimum observable x-ray spacings. These changes proved partly reversible on diluting the solutions, and measurements of crystal volume and minimums x-ray spacing were used to follow denaturation and renaturation as a function of concentration for several denaturants. Some of these, including bromoethanol and sodium dodecyl sulfate, had little effect on the crystals below critical concentrations at which there was a sharp volume increase and loss of x-ray pattern, which could, however, be regenerated to about 3.2-A resolution. Others, including KCNS and urea, caused more gradual changes, but with a smaller degree of recovery. It is suggested that at least two different denaturation mechanisms are involved with detergent-like reagents disrupting the hydrophobic interactions joining the two wings of the lysozyme molecule and hydrophilic denaturants interacting primarily with polar groups on the molecular surface.
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PMID:Crystallographic studies of protein denaturation and renaturation. 1. Effects of denaturants on volume and X-ray pattern of cross-linked triclinic lysozyme crystals. 55 40

Native lysozyme and three reduced derivatives (carboxymethyl, carboxamidomethyl, and triphenylethyl-phosphonium) were examined by circular dichroism, and fractions of the protein chain present as alpha-helix, beta structure, and unordered structure were estimated by a computeradapted curve-fitting program. The alpha helix ranged from 2 to 23% in the three products, while native lysozyme exhibited 26 to 31%. However, beta structure in the reduced samples occupied 23-62% of the chain length (the latter in 50% methanol), consistently in excess of the native content(11-16%). Secondary structure in the reduced samples increased with pH, while that of the native protein remained nearly constant. In 8 M urea alpha helix was mostly eliminated from the reduced protein, while beta structure was nearly unaffected. Qualitatively, a partial loss of beta structure appeared to result from peptic digestion of the reduced samples, with further loss on exposure of the digest to urea. Stability of the observed beta structure indicates its existence prior to the oxidation of SH groups, which is concomitant with development of the native conformation. This structure could, therefore, constitute at least part of a precursor conformation in the formation of native structure.
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PMID:Studies on secondary structure in chicken egg-white lysozyme after reductive cleavage of disulfide bonds. 77 35

Conformational studies on an isolated integral membrane protein are reported. Lipoprotein of Escherichia coli outer membrane was released from murein by treatment with either lysozyme or trypsin. The isolated lysozyme-released lipoprotein (lipoprotein I) contained 2 or 3 muropeptides covalently linked at the C-terminal end, while the trypsin-released lipoprotein (lipoprotein II) was free of muropeptides and lacked the C-terminal peptide Tyr-Arg-Lys. Circular dichroism spectra of the two preparations were essentially identical, and they show an alpha-helix content of about 80%. According to calculations based on the Chou-Fasman rules for proteins of known sequence, lipoprotein is 64% alpha-helix and 15% beta-structure. Infrared spectroscopy qualitatively supports these values. The conformation was stable in the pH range of 5 - 12. Danaturation of lipoprotein by heat, 8 M urea, or sodium dodecylsulphate was a fully reversible, cooperative process. The thermal denaturation of lipoprotein occurs in two steps with transition points at 79.4 degrees C for lipoprotein I and at 85.1 degrees C for lipoprotein II. Lioprotein markedly changes conformation at dodecylsulphate concentrations where micelle formation sets in. The unusual behaviour of the lipoprotein convormation in sodium dodecylsulphate is discussed in relation to the lipoprotein conformation and aggregation within the membrane.
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PMID:Conformational studies on murein-lipoprotein from the outer membrane of Escherichia coli. 79 57

The protoplasts of a mutant of Bacillus subtilis 168 (B. subtilis CMK33) are osmotically fragile when compared to protoplasts of the parent organism and contain an active, membrane-associated phospholipase A1. A protein found in the parent organism specifically inhibits the phospholipase A1 (Kent, C., and Lennarz, W.J. (1972) Proc. Nat. Acad. Sci. U.S.A. 69, 2793-2797). The inhibitor exists in both a soluble and particulate form. The soluble inhibitor is not found in the cytoplasm, but rather in a "periplasmic" fraction released from the cell during incubation with lysozyme. The soluble inhibitor has been purified to homogeneity by diethylaminoethyl-cellulose and hydroxylapatite chromatography. Its molecular weight is 28,000 to 32,000 as determined by gel filtration chromatography and 36,000 to 37,000 as determined by sodium dodecyl sulfate-urea gel electrophoresis. The inhibitor appears to inactivate the membrane bound phospholipase A1 by an enzymatic process that is dependent on time and protein concentration. Binding of the inhbitor to the membrane-associated phospholipase cannot be detected. When purified inhibitor is added to cells of B. subtilis CMK33 during treatment with lysozyme, the osmotic stability of the resultant protoplasts is similar to that of protoplasts of the wild type of organism.
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PMID:Purification and characterization of an inhibitor of phospholipase A1 in Bacillus subtilis. 80 82

Reaction of alpha-lactalbumin at pH 7 in aqueous solution with either 2-hydroxy-5-nitrobenzylbromide or N-bromosuccinimide yields derivatives in which only 2 of the 4 tryptophan residues are modified. All 4 residues of tryptophan are modified under the similar conditions in 8 M urea. Structural analysis of the modified derivatives revealed that tryptophans 26 and 118 are the sole reactive residues and that tryptophan 118 reacts more rapidly than tryptophan 26. The fluorescence of alpha-lactalbumin modified to varying extents with N-bromosuccinimide indicates that tryptophan 118 is exposed to solvent whereas tryptophan 26 is in a more hydrophobic environment. The chemical reactivities and fluorescence properties of tryptophans 26 and 118 are consistent with the proposed conformations of alpha-lactalbumin based on its similarity with egg white lysozyme. The kinetic properties of both derivatives of alpha-lactalbumin containing up to 2 modified residues indicate that each derivative has decreased affinity for the galactosyltransferase but that at saturating concentrations, Km and Vmax for lactose synthesis are unchanged from those of native alpha-lactalbumin.
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PMID:Modification of bovine alpha-lactalbumin with N-bromosuccinimide and 2-hydroxy-5-nitrobenzylbromide. 80 37

Human supragingival dental plaque was collected from patients with various degrees of caries and periodontal disease. Plaque extracts, prepared in five different solutions (four varied from pH 1.8 to 12.7; one contained urea), were analyzed by polyacrylamide gel electrophoresis, and tested for amylase and lysozyme enzyme activity. Because no qualitative or quantitative advantages of using the extremes of pH or urea were observed, all subsequent extracts were prepared in phosphate buffered saline at pH 7.3. Concentrated extracts were fractionated by gel filtration and characterized by polyacrylamide gel electrophoresis, peptide mapping, molecular weight estimation, determination of enzymatic activities and amino acid and carbohydrate analyses. Regions of similarity among the gels were revealed by comparing the electrophoretic patterns of pooled plaque extract, normal serum and whole saliva. The elution pattern of pooled plaque extract from a standardized Sephadex G-200 column indicated the presence of both high and low molecular weight proteins that might have correlated with the components of normal serum and saliva. A predominant and dialyzable third fraction had no correlate in either serum or saliva. The small peptides in this fraction were subjected to amino acid, carbohydrate and peptide map analyses. The most abundant amino acids were alanine, glutamic acid, glycine, valine, leucine, lysine and serine. These small components contained no neutral or amino sugars. Pooled plaque extract and the small peptides exhibited similar peptide maps.
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PMID:Studies on human dental plaque. 1. Physical and chemical characteristics and enzyme activities of pooled plaque extracts. 80 55

Formation of opaque deposits on the anterior (air) surface of hydrophilic soft contact lenses is a problem worthy of investigation by all concerned. These deposits have been analyzed for biomaterials by chemical, biochemical, electrophoretic, and immunological techniques. Qualitative and quantitative chemical colorimetric tests revealed the presence of variable amounts of protein (5-10 microgram/lens), carbohydrate (1.0-1.2 microgram/lens), and phospholipids (0.01-0.05 micronmole/lens). Cholesterol and glucose were not present at detectable levels. Fluorescent antibody tests with appropriate controls gave positive tests for albumin, lysozyme, gamma-G-globulin, and alpha1-lipoprotein in the deposits, all proteins present in tear fluid. Deposits were most effectively removed from the lenses by the combination of heat, sodium dodecyl sulfate (SDS) detergent, and the thiol reagent dithiothreitol (DTT). SDS-denatured protein migrated on polyacrylamide gels with electrophoretic patterns corresponding to molecular weights for those proteins detected by the above antibody tests. The nature of the bonding interactions of biomaterials to the lenses was probed by chemical reagents used to remove them, employed singly and in all possible combinations. Urea, guanidine hydrochloride, potassium thiocyanate, potassium perchlorate, hydroxylamine, and EDTA were much less effective than SDS and DTT. These data suggest that apolar interactions plus disulfide bonds may be important in stabilizing the deposit structure, and point to improved cleaning procedures.
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PMID:Analysis of biomaterials deposited on soft contact lenses. 87 44

Upon preincubation with urea, various 3- or 4-substituted N-methylpyridinium salts form charge-transfer complexes with tryptophan containing proteins such as, L-chymotrypsin and lysozyme. The complexes were studied by using the difference spectrophotometric technique. The fluorescence examination showed that tryptophyl residues in protein molecules are engaged in the complex formation process. The complex formation reactions proceed at a considerable rate. The stopped-flow method was used to determine the pseudo first order rate constants. A linear dependence of the pseudo first order rate constants with the donor concentration was found. The second order rate constants were obtained by dividing the mean value of the pseudo first order rate constants by the initial donor concentration for each run. The linear dependence of second order rate constants with the electron affinity of the acceptors can serve as a criterion for the formation of charge-transfer complexes.
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PMID:The kinetics of complex formation of tryptophan containing proteins with pyridinium salts. 121 82

The influence of urea and of guanidine chloride on the binding of the bacterial substrate and of inhibitors such as N-acetylglucosamine or chitotetraose to hen lysozyme were studied at 20 degrees and at 40 degrees C (physiological temperature). The action of urea did not prevent a certain degree of organization of the enzyme compatible with its usual behaviour in the presence of some inhibitors and with its crystallization ; guanidine chloride, already at low concentrations, seemed to have a more severe effect on lysozyme.
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PMID:The influence of urea and guanidine chloride on the binding of the binding of the bacterial substrate and inhibitors to hen lysozyme at physiological temperature (40 degrees) (*). 124 Dec 84


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