title: Mechanism of action and structural properties of an intracellular alpha-glucosidase from Thermoascus aurantiacus Miehe.
abstract: The intracellular alpha-glucosidase purified from the mycelium of Th. aurantiacus is an exceptionally stable protein which displays its maximum activity at 70 degrees C and pH 4.2 and is inhibited by 4 M urea, 0.5 M mercaptoethanol, 15 mM Cu++ and 0.04% rose bengal only after incubation at high temperature (60-70 degrees C). Carboxylic groups with pKa = 3.25 appear involved in the catalytic process together with a histidine residue (pKa = 5.7). Plots of Log V vs pH also show that the carboxylic groups dissociate in a cooperative way. A simple reaction mechanism is proposed on the basis of competitive inhibition by delta-gluconolactone, which suggests the formation of a carbonium ion.
mesh_terms: D001203:Ascomycota / Q000201:enzymology*; D002384:Catalysis; D055598:Chemical Phenomena; D002621:Chemistry; D005947:Glucose / Q000494:pharmacology; D005959:Glucosidases / Q000378:metabolism*; D065089:Glycoside Hydrolase Inhibitors; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008623:Mercaptoethanol / Q000494:pharmacology; D012395:Rose Bengal / Q000494:pharmacology; D013696:Temperature; D014508:Urea; D000520:alpha-Glucosidases / Q000378:metabolism*
chemical_list: D065089:Glycoside Hydrolase Inhibitors; D012395:Rose Bengal; D008623:Mercaptoethanol; D014508:Urea; D005959:Glucosidases; D000520:alpha-Glucosidases; D005947:Glucose