Mechanism of action and structural properties of an intracellular alpha-glucosidase from Thermoascus aurantiacus Miehe
Bedino, S.; Testore, G.; Obert, F.
Italian Journal of Biochemistry 32(6): 408-417
1983
ISSN/ISBN: 0021-2938 PMID: 6373662 Document Number: 213039
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.