title: Kinetic properties and mechanism of action of an intracellular beta-glucosidase from Thermoascus aurantiacus Miehe.
abstract: Intracellular beta-glucosidase is strongly inhibited by its own substrate p-nitrophenyl-beta-glucoside which displays high affinity for two binding sites. A non-productive complex is formed also by cellobiose, but its lower affinity results in a much lower inhibition. As shown by inhibition experiments performed with glucono-delta-lactone, the hydrolytic reaction proceeds through the formation of a carbonium ion, very similar in its half-chair conformation to the delta-lactone. Carboxylic groups (pK = 3.19) appear involved in the catalytic process together with a histidine residue (pK = 5.64): while the carboxylate ions stabilize the carbonium ion, the displaced group accepts a proton from the protonated imidazole.
mesh_terms: D002475:Cellobiose / Q000378:metabolism; D003593:Cytoplasm / Q000201:enzymology; D005658:Fungi / Q000201:enzymology*; D005942:Gluconates / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D005959:Glucosidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005960:Glucosides / Q000378:metabolism*; D006027:Glycosides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007783:Lactones; D010777:Photochemistry; D012395:Rose Bengal / Q000494:pharmacology
chemical_list: D005942:Gluconates; D005960:Glucosides; D006027:Glycosides; D007783:Lactones; D002475:Cellobiose; D012395:Rose Bengal; D005959:Glucosidases; D005947:Glucose; C010730:beta-glucono-1,5-lactone