Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

The reversible unfolding of alpha-lactalbumin by guanidine hydrochloride, was studied at 25.0 degrees C in a relatively low concentration range of the denaturant (0.80-2.00 mol/l) by means of difference spectra and pH-jump measurements. The unfolding was shown to occur between two states, N and D, because apparent rate-constants of the unfolding and the refolding reactions depended only on pH. All curves plotted as the logarithmical equilibrium constant log KD against pH could fall on the same base curve by shifting each curve along the log KD axis. From the dependence of the logarithmic rate constant on pH, master curves could also be made for the forward and the backward reactions. The dependence of these master curves on pH indicates that the groups affecting the pH dependence of the unfolding are three residues with pKN = 3.3 and pKA = pKD = 4.4, one residue with pKN = pKA = 3.8 and pKD = 4.4, and one residue with pKN = 5.8 and pKA = pKD = 6.3, where A indicates the activated state. On the other hand, from the denaturant activity dependence of the shift factors required for making the master curves, the value of the intrinsic binding constant of the denaturant to the protein was found to be similar to that obtained from previous measurements at pH 5.5. Differences between the numbers of the binding sites of the denaturant on the denaturated and the native proteins, and between those on the activated and the native proteins were shown to be 5.3 and 2.1, respectively. The free energy of stabilization in the native-like environment also shows that the protein in the native state is more unstable than lysozyme.
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PMID:Equilbrium and kinetics of the unfolding of alpha-lactalbumin by guanidine hydrochloride (II). 0 10

The luminescence of bovine alpha-lactalbumin at 77 K has been studied and compared with that of lysozyme. Alpha-Lactalbumin has several unusual properties, including a fluorescence spectrum showing vibrational fine structure, an abnormal phosphorescence spectrum, a high fluorescence: phosphorescence ratio and an abnormal phosphorescence decay. These properties are largely due to the proximity of tryptophan residues to disulphide bonds. Reduction of all these bonds causes considerable changes in alpha-lactalbumin luminescence, as does denaturation in acid solution. Reduction of a single labile disulphide bond has little effect, and the properties of alpha-lactalbumin III, a variant lacking one disulphide bond and one trypotophan residue, are similar to those of the normal protein. Several differences between alpha-lactalbumin and lysozyme are reported. The results support the suggestion that the two tryptophan residues found in the active site cleft of alpha-lactalbumin may be largely responsible for its luminescence.
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PMID:The low-temperature luminescence properties of bovine alpha-lactalbumin. 23 14

Modification of hen egg-white lysozyme by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide in presence of 4-phenylbutylamine yielded derivatives, which contained 0.6--0.7 modified residues and retained about 60% of the original activity. Kinetic studies revealed that the modified-lysozyme increases approx. 20-fold the kcat of hydrolysis of SucGly2Phe-4-nitroanilide by alphachymotrypsin, without changing the Km. The apparent dissociation constant of phenylbutylamine-modified lysozyme . chymotrypsin complex was found to be 0.03 mM and independent of substrate concentration. The accelerating effect of the modified lysozyme was also observed with other p-nitroanilide substrates of alpha-chymotrypsin. However, the hydrolysis of other substrates, acylation by active site titrant or inhibition by irreversible or competitive inhibitors were uneffected. The enhancing effect of the modified lysozyme seems to be very specific since other chymotrypsin-like enzymes, or serine proteinases except delta-chymotrypsin, were not influenced and phenylbutylamine derivatives of alpha-lactalbumin or ribonuclease were lacking any enhancing effect. Smaller, but significant enhancing effect was found also in lysozyme substituted by benzylamine, beta-phenylethylamine and tryptamine and in inactive derivatives of lysozyme substituted by phenylbutylamine. Competitive inhibitors of lysozyme such as N-acetyl-D-glucose amine oligomers, (GlcNAc)2 and (GlcNAc)3 abolished partially the accelerating effect of phenylbutylamine-modified lysozyme, indicating that the substituted group is located in the vicinity of the binding site.
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PMID:Enhancement of alpha-chymotrypsin-catalyzed hydrolysis of specific p-nitroanilide substrates by 4-phenylbutylamine derivative of hen egg-white lysozyme. 71 65

As the lysozyme story continues to unfold, rheumatic disease is one area where the study of this fascinating protein will be most important. The special biochemical features of lysozyme--its hexosaminidase function, its ability to bring about transglycosylation, its homology to alpha-lactalbumin, and its cationic nature--suggest that the connective tissues may prove to be the key to the understanding of the function of lysozyme. As methods for its accurate measurement become standardized, better data on the activity of the enzyme in various tissues and body fluids, in both health and disease, will be forthcoming. As additional studies are done to ascertain which of the hypothetical functions attributed to lysozyme are of significance in vivo, it will be the student of the connective tissues and the diseases thereof who can be expected to profit most from an udnerstanding of the role of lysozyme in mammalian biology.
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PMID:Connective tissue lysozyme in health and disease. 78 4

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

We have attempted to detect binding of N-acetylglucosamine (NAG) to alpha-lactalbumin, the B protein of lactose synthetase, under conditions in which binding of NAG to lysozyme, a protein to which alpha-lactalbumin has a significant sequence homology, is observed. Using 1H nuclear magnetic resonance spectroscopy, uv difference spectroscopy, competition of NAG with N-methylnicotinamide chloride, and fluorescence spectroscopy, no binding was detected. The synthesis of a NAG analogue, N-diazoacetyl-glucosamine (diazoNAG), was carried out, and the molecule was demonstrated to be an active galactose acceptor in the lactose synthetase reaction. Use of this molecule in photochemical labeling experiments resulted in a large amount of nonspecific labeling of alpha-lactalbumin, lactose synthetase A protein, ribonuclease, and lysozyme, but competition experiments in the presence of an excess of NAG revealed some specific labeling in the case of A protein and lysozyme, but not with alpha-lactalbumin or a ribonuclease control. Thus, it is highly questionable that a NAG binding site is retained in alpha-lactalbumin; furthermore, it appears that the galacyosyl acceptor makes significant contacts with the A protein rather than alpha-lactalbumin in the lactose synthetase complex.
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PMID:The interaction of N-acetylglucosamine and an affinity-label analogue with alpha-lactalbumin and lactose synthetase. 81 Dec 54

Circular dichroism spectra have been obtained for albumin, alpha-chymotrypsinogen, collagen, concanavalin A, elastase, hemoglobin, histone f2b, alpha-lactalbumin, lactate dehydrogenase, beta-lactoglobulin, lysozyme, myoglobin, papain, ribonuclease A, and thermolysin in the presence of sodium dodecyl sulfate and dithiothreitol. While all spectra have the shape anticipated for a mixture of random coil and alpha helix, the intensities differ markedly ([theta]222 ranges from --1400 to --15 000 deg cm2/dmol). The variation in the circular dichroism can be quantitatively explained by a model which assumes that the arginyl, histidyl, and lysyl residues have an enhanced probability of propagating a helical segment in the presence of the detergent. The model also permits the computation of dimensional properties (unperturbed end-to-end distance and radius of gyration) for polypeptides of known amino acid sequence. Such computations have been performed for 67 proteins. The computed dimensions are compatible with experimental values and with the molecular weight dependence of the transport properties of the complexes. Furthermore, the model can account for the abnormal transport properties of the sodium dodecyl sulfate complexes formed by ribonuclease A, collagen fragments, and histones f2a1, f2a2, f2b, and f3. Even though some of the protein--sodium dodecyl sulfate complexes have helical contents as high as 50%, their overall conformation more closely approximates that of a random coil than a rod.
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PMID:Conformational properties of the complexes formed by proteins and sodium dodecyl sulfate. 96 36

A new rapid method for the quantitative and routine determination of free amino groups in intact pure proteins has been developed. Primary amino groups are labeled with fluorescamine and the labeled groups are detected by absorption spectroscopy in the range 375-390 nm. The amino group concentration can be determined in a few minutes without hydrolyzing the labeled protein and extracting a lysine derivative. The method was tested with the following proteins: lysozyme, alpha-lactalbumin, beta-lactoglobulin, bovine serum albumin, ribonuclease, ribonuclease-S-peptide, and alphasl-casein B. Application of this method to the estimation of available lysine is discussed.
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PMID:New method for determination of free amino groups in intact pure proteins: relationship to available lysine. 99 78

The deuteration of the tryptophan residues of hen egg white lysozyme, bovine alpha-lactalbumin and bovine beta-lactoglobulin in d-TFA has been studied by PMR spectroscopy. It is found that short times of exposure to d-TFA allow selective deuteration at the C-2 position with only a small amount of deuteration at the C-5 position, as expected from studies on model peptides described in the previous paper. The proteins studied essentially regained their native structures after the treatment, except for broadening and shifting of the histidine resonances in the case of alpha-lactalbumin. Selective deuteration at the tryptophan C-2 position was readily observed by difference spectroscopy of the denatured protein, but PMR difference spectra of the same proteins in benign solvents did not contain resonances from all of the exchanged protons. Some resonances would not be observed because of line broadening, which causes the resonances to fall below the limit of sensitivity of detection at 100 MHz. Deuteration by brief exposure to d-TFA should be useful for the identification of tryptophan resonances in the PMR spectra of native proteins. The deuteration of all the aromatic protons of tryptophan residues in proteins by immersion in d-TFA for 4 hours at room temperature was studied. This technique is unlikely to be of general use for the simplification of the aromatic region of the PMR spectra of native proteins because of the degradation of tryptophan residues which results from the acid treatment.
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PMID:Proton magnetic resonance spectroscopic studies of proteins containing deuterated tryptophan residues. 100 98

Analysis of the time decay of fluorescence anisotropy of 1-dimethylaminoaphthalene-5-sulfonyl (DNS) and fluorescamine derivatives of bovine alpha-lactalbumin and lysozyme reveals that no significant differences in mean rotational relaxation times are present. While fluorescamine molecules appear to orient randomly on these proteins, DNS is bound with a preferential orientation. Other fluorescence characteristics of the labels are also cited.
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PMID:A comparative study on bovine alpha-lactalbumin and lysozyme by nanosecond fluorometry. 126 Jan 1


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