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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)

Artificial membranes bearing immobilized enzymes can be used to study some effects of membrane structure on enzyme kinetic behavior. The bienzyme system described is a mixture of beta-glucosidase and glucose oxidase. Gluconolactone, the product of thesecond enzyme, is an inhibitor of the first one. The resulting feedback effect has been compared using a mixed two-enzyme membrane, two separated one-enzyme membranes, and astirred bienzyme solution. The feedback effect is quicker and more efficient in the two-enzyme membrane than in solution; it is slower and less efficient in the case of the separated one-enzyme membranes. Effects of enzyme proximity in the structure are discussed. Conclusions are drawn concerning the efficiency of feedback mechanisms when enzymes are embedded within a single structure.
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PMID:The kinetic behavior of an artificial bienzyme membrane. 114 Dec 41

The kinetics of pNPG, pNPX and cellobiose hydrolysis by beta-glucosidase cloned from C. thermocellum into E. coli was studied. The V values for these substrate hydrolysis are 102, 357 and 6.7 mumols/min/mg protein, respectively; Km are 0.44 mM, 50 mM and 100 mM, respectively, sigma-Gluconolactone inhibits the hydrolysis of all substrates according to a competitive mechanism with Ki of 0.032 mM, 6.0 mM and 0.25 mM, respectively. Glucose inhibits the hydrolysis of pNPG and pNPX also via a competitive mechanism with Ki of 10 mM and 37 mM, while cellobiose--via a mixed type mechanism with Ki of 110 mM and 350 mM. The existence of separate adsorption sites for each substrate and of a common catalytic site for pNPG and pNPX hydrolysis is supposed.
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PMID:[Various kinetic properties of beta-glucosidase cloned from Clostridium thermocellum in E. coli]. 211 22

Three binding sites on highly purified lysosomal beta-glucosidase from human placenta were identified by studies of the effects of interactions of various enzyme modifiers. The negatively charged lipids, taurocholate and phosphatidylserine, were shown to be noncompetitive, nonessential activators of 4-methylumbelliferyl-beta-D-glucoside hydrolysis. Similar results were observed using the natural substrate, glucosyl ceramide, and low concentrations of taurocholate (less than 1.8 mM) or phosphatidylserine (0.5 mM). However, higher concentrations resulted in a complex partial inhibition of glucosyl ceramide hydrolysis. Increasing concentrations of phosphatidylserine obviated the effects of taurocholate, suggesting that these compounds compete for a common binding site on the enzyme. Glucosyl sphingosine and its N-hexyl derivative were potent noncompetitive inhibitors of the enzyme activity using either substrate. Taurocholate (or phosphatidylserine) and glucosyl sphingosine were shown to be mutually exclusive, indicating competition for a common binding site. In contrast, octyl- and dodecyl-beta-glucosides were linear-mixed-type inhibitors of glucosyl ceramide or 4-methylumbelliferyl-beta-D-glucoside hydrolysis, indicating at least two binding sites on the enzyme. Inhibition by these alkyl beta-glucosides was observed only in the presence of taurocholate or phosphatidylserine. The competitive component [Ki (slope)] for the two alkyl beta-glucosides decreased with increasing alkyl chain length, and was unaffected by increasing taurocholate or phosphatidylserine concentration. The noncompetitive component [Ki (intercept)] was nearly identical for both alkyl beta-glucosides and was decreased by increasing taurocholate or phosphatidylserine concentration. These results indicated that the negatively charged lipids and alkyl beta-glucosides were not mutually exclusive, but interacted with different binding sites on the enzyme. Gluconolactone was shown to protect the enzyme from inhibition by the catalytic site-directed covalent inhibitor, conduritol B indicating an interaction at a common binding site. In the presence of substrate, taurocholate facilitated the inhibition of gluconolactone or conduritol B epoxide. These studies indicated that lysosomal beta-glucosidase had at least three binding sites: (i) a catalytic site which cleaves the beta-glucosidic moiety, (ii) an aglycon site which binds the acyl or alkyl moieties of substrates and some inhibitors, and (iii) a hydrophobic site which interacts with negatively charged lipids and facilitates enzyme catalysis.
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PMID:Human lysosomal beta-glucosidase: kinetic characterization of the catalytic, aglycon, and hydrophobic binding sites. 642 91