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:3.2.1.21 (beta-glucosidase)
3,280 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The problem of melaninogenesis and quinone tanning of the cuticle was examined by histochemical and biophysical methods (electroparamagnetic resonance: EPR) on normal subjects of Pycnoscelus surinamensis and on subjects with abnormal cuticular colour. The cuticle of abnormal subjects showed a lower content of polyphenolic substances and a greater positivity for the indole group. This suggests that in these insects tanning products can be synthetized differently and not derived from tyrosine but from tryptophan as postulated by Pryor (1955). Furthermore, a higher number of unsaturated aminic groups is found in abnormal subjects. Granules present only in the cytoplasm of the epidermal cells of the abnormal newly moulted subjects may indicate that the polyphenolic compound of tanning, secreted in an inactive form as 4-0, beta-glucoside, is not freed from the beta-glucosidase and remains as such in the cytoplasm.
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PMID:Histochemical and biophysical study of cuticle sclerotization in Pycnoscelus surinamensis L. (Blattaria). 4 33

The problem of melaninogenesis and quinone tanning of the cuticle was examined by histochemical and biophysical methods (electroparamagnetic resonance: EPR) on normal subjects of Pycnoscelus surinamensis and on subjects with abnormal cuticular colour. The cuticle of abnormal subjects showed a lower content of polyphenolic substances and a greater positivity for the indole group. This suggests that in these insects tanning products can be synthetized differently and not derived from tyrosine but from tryptophan as postulated by Pryor (1955). Furthermore, a higher number of unsaturated aminic groups is found in abnormal subjects. Granules present only in the cytoplasm of the epidermal cells of the abnormal newly moulted subjects may indicate that the polyphenolic compound of tanning, secreted in an inactive form as 4-O, beta-glucoside, is not freed from the beta-glucosidase and remains as such in the cytoplasm.
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PMID:Histochemical and biophysical study of cuticle sclerotization in Pycnoscelus surinamensis L. (Blattaria). 53 16

The activity and stability of some enzymes of Asp. awamori cellulolytic complex were studied as affected by chemical modification of carboxylic groups with N,N'-dicyclohexyl carbodiimide (DCCD) and amine groups with glutaric aldehyde. The carboxylic groups are established to be necessary for manifestation of the activities of C1- and C2-cellulases, Cx-exo- and Cx-endoglucanases. Their role is negligible in the action of beta-glucosidase. The activity of individual cellulases was studied as affected by nucleophilic substitution of DCCD-activated COOH-groups by various reagents (glycine amide, leucine amide, tyrosine amide and N-benzoyl-l-arginine-methyl ether-hydrochloride). Tyrosine amide is the least inacting reagent for all the enzymes, glycine amide is somewhat more activating. Essential differences are shown in the chemical and catalytic properties of Cx-exoglucanase and beta-glucosidase. It is found (under the effect of glutaric aldehyde) that amino groups are significant for manifestation of the activities of C1- and C2-cellulases and Cx-endoglucanase and to a less extent for that of Cs-exoglucanase and beta-glucosidase. It is supposed that electrostatic interactions of the carbolytic and amine groups might be an essential factor for stability of C1- and C2-cellulases and Cx-endoglucanase.
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PMID:[Modification of the carboxyl and amine groups of the cellulolytic enzymes of Aspergillus awamori]. 102 13

Modification of A. conoides beta-glucosidase by diethylpyrocarbonate caused rapid inactivation of the enzyme. The kinetic analyses showed that the inactivation by diethylpyrocarbonate resulted from the modification of an average of one histidine residue per mole of enzyme. The modified enzyme showed an increase in absorbance at 240 nm. Sulphydryl, lysine and tyrosine residues were not modified by diethylpyrocarbonate treatment. The substrate offered significant protection against diethylpyrocarbonates modification. The results indicate that diethylpyrocarbonate was interacting with the enzyme at or near the active site.
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PMID:Inactivation of a beta-glucosidase from Arthrobotrys conoides by diethyl pyrocarbonate: evidence of histidine at the active site. 152 73

The beta-glucosidase from Schizophyllum commune was purified to homogeneity by a modified procedure that employed Con A-Sepharose. The participation of carboxyl groups in the mechanism of action of the enzyme was delineated through kinetic and chemical modification studies. The rates of beta-glucosidase-catalyzed hydrolysis of p-nitrophenyl-beta-D-glucoside were determined at 27 degrees C and 70 mM ionic strength over the pH range 3.0-8.0. The pH profile gave apparent pK values of 3.3 and 6.9 for the enzyme-substrate complex and 3.3 and 6.6 for the free enzyme. The enzyme is inactivated by Woodward's K reagent and various water-soluble carbodiimides; chemical reagents selective for carboxyl groups. Of these reagents, 1-ethyl-3-(4-azonia-4,4-dimethylpentyl)carbodiimide iodide in the absence of added nucleophile was the most effective and a kinetic analysis of the modification indicated that one molecule of carbodiimide is required to bind to the beta-glucosidase for inactivation. Employing a tritiated derivative of the carbodiimide, 44 carboxyl groups in the enzyme were found to be labelled while the competitive inhibitor deoxynojirimycin protected three residues from modification. Treatment of the enzyme with tetranitromethane resulted in the modification of five tyrosine residues with approx. 28% diminution of enzymic activity. Titration of denatured enzyme with dithiobis(2-nitro-benzoic acid) indicated the absence of free thiol groups. Reaction of the enzyme with diethyl pyrocarbonate resulted in the modification of four histidine residues with the retention of 78% of the original enzymatic activity. The divalent transition metals Cu2+ and Hg2+ were found to be potent inhibitors of the enzyme, binding in an apparent irreversible manner.
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PMID:Chemical modification of a beta-glucosidase from Schizophyllum commune: evidence for essential carboxyl groups. 211 26

The role of exposed tyrosine side-chains in enzyme-catalyzed reaction by sweet almond emulsin beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) has been studied using N-acetylimidazole as the specific reagent. The changes in activity, binding affinity and kinetic parameters (Km, V) as a result of acetylation of the phenolic hydroxyl groups have been determined. The acetylation increased the Km values of both beta-glucosidase and beta-galactosidase activities, whereas V remained unchanged. Similarly, the binding affinity for immobilized phenyl beta-D-glucopyranoside decreased appreciably. After the removal of the acetyl groups the enzyme regained 96% of the original activity. It is concluded that the tyrosine moieties, located in the active centre of the enzyme, have both glucoside and galactoside binding functions.
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PMID:Study on the role of tyrosine side-chains at the active centre of emulsin beta-D-glucosidase. 679 75

The beta-glucosidase from Agrobacterium sp. catalyzes the hydrolysis of beta-glucosides via a covalent alpha-D-glucopyranosyl-enzyme intermediate involving Glu358. Hydrolysis of 2,4-dinitrophenyl beta-D-glucopyranoside by the low activity Glu358Asp mutant of Agrobacterium beta-glucosidase is accompanied by time-dependent inactivation of the enzyme. Through kinetic studies, labeling, and sequence analysis, inactivation is shown to be a consequence of the occasional (1 time in 1100) attack of Tyr298 on the anomeric center of the substrate, in place of the catalytic nucleophile, with formation of a stable alpha-D-glucopyranosyl tyrosine residue. Tyr298 is conserved throughout family 1 of glycoside hydrolases, an indication of a possible role in catalysis. Results of a kinetic analysis of the Tyr298Phe mutant are consistent with a function of Tyr298 in both orienting the nearby nucleophile Glu358 and stabilizing its deprotonated state in the free enzyme.
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PMID:Substrate-induced inactivation of a crippled beta-glucosidase mutant: identification of the labeled amino acid and mutagenic analysis of its role. 757 60

Chemically modified forms of egg-white avidin and bacterial streptavidin (termed nitro-avidin and nitro-streptavidin, respectively), in which the binding-site tyrosine was nitrated, were used for several biotechnological applications. The fundamental difference between nitro-avidin and the native protein is that interaction of the modified protein with biotin can be reversed under relatively mild conditions. Consequently, nitro-avidin affinity columns or immobilizing matrices can be reused. Three examples are given to demonstrate the possible uses of such columns: (a) biotinylated protein A was attached to a nitro-avidin affinity column, and immunoglobulin was purified directly from whole rabbit serum; (b) biotinylated transferrin was attached to a nitro-streptavidin column, and anti-transferrin was isolated directly from rabbit anti-serum; and (c) biotinylated beta-glucosidase was immobilized onto a nitro-avidin column and used as an enzyme reactor. In each example, the immobilized biotinylated probe could be released selectively from the column and recovered following its utilization. Reusable nitro-avidin thus provides an easy and attractive reversible form of avidin and thereby serves to expand the versatility of avidin-biotin technology.
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PMID:Immobilized nitro-avidin and nitro-streptavidin as reusable affinity matrices for application in avidin-biotin technology. 895 58

Enzymatic transglycosylation of lactose into oligosaccharides was studied using wild-type beta-glucosidase (CelB) and active site mutants thereof (M424K, F426Y, M424K/F426Y) and wild-type beta-mannosidase (BmnA) of the hyperthermophilic Pyrococcus furiosus. The effects of the mutations on kinetics, enzyme activity, and substrate specificity were determined. The oligosaccharide synthesis was carried out in aqueous solution at 95 degrees C at different lactose concentrations and pH values. The results showed enhanced synthetic properties of the CelB mutant enzymes. An exchange of one phenylalanine to tyrosine (F426Y) increased the oligosaccharide yield (45%) compared with the wild-type CelB (40%). Incorporation of a positively charged group in the active site (M424K) increased the pH optimum of transglycosylation reaction of CelB. The double mutant, M424K/F426Y, showed much better transglycosylation properties at low (10-20%) lactose concentrations compared to the wild-type. At a lactose concentration of 10%, the oligosaccharide yield for the mutant was 40% compared to 18% for the wild-type. At optimal reaction conditions, a higher ratio of tetrasaccharides to trisaccharides was obtained with the double mutant (0.42, 10% lactose) compared to the wild-type (0.19, 70% lactose). At a lactose concentration as low as 10%, only trisaccharides were synthesized by CelB wild-type. The beta-mannosidase BmnA from P. furiosus showed both beta-glucosidase and beta-galactosidase activity and in the transglycosylation of lactose the maximal oligosaccharide yield of BmnA was 44%. The oligosaccharide yields obtained in this study are high compared to those reported with other transglycosylating beta-glycosidases in oligosaccharide synthesis from lactose.
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PMID:Improved oligosaccharide synthesis by protein engineering of beta-glucosidase CelB from hyperthermophilic Pyrococcus furiosus. 1125 2

Human cytosolic beta-glucosidase (hCBG) is a xenobiotic-metabolizing enzyme that hydrolyses certain flavonoid glucosides, with specificity depending on the aglycone moiety, the type of sugar and the linkage between them. Based upon the X-ray structure of Zea mays beta-glucosidase, we generated a three-dimensional model of hCBG by homology modelling. The enzyme exhibited the (beta/alpha)(8)-barrel fold characteristic of family 1 beta-glucosidases, with structural differences being confined mainly to loop regions. Based on the substrate specificity of the human enzymes, sequence alignment of family 1 enzymes and analysis of the hCBG structural model, we selected and mutated putative substrate (aglycone) binding site residues. Four single mutants (Val(168)-->Tyr, Phe(225)-->Ser, Tyr(308)-->Ala and Tyr(308)-->Phe) were expressed in Pichia pastoris, purified and characterized. All mutant proteins showed a decrease in activity towards a broad range of substrates. The Val(168)-->Tyr mutation did not affect K (m) on p -nitrophenyl ( p NP)-glycosides, but increased K (m) 5-fold on flavonoid glucosides, providing the first biochemical evidence supporting a role for this residue in aglycone-binding of the substrate, a finding consistent with our three-dimensional model. The Phe(225)-->Ser and Tyr(308)-->Ala mutations, and, to a lesser degree, the Tyr(308)-->Phe mutation, resulted in a drastic decrease in specific activities towards all substrates tested, indicating an important role of those residues in catalysis. Taken together with the three-dimensional model, these mutation studies identified the amino-acid residues in the aglycone-binding subsite of hCBG that are essential for flavonoid glucoside binding and catalysis.
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PMID:Substrate (aglycone) specificity of human cytosolic beta-glucosidase. 1266 41


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