Essential groups and stability of α-glucosidase ofPenicillium notatum

Abstract

α-Glucosidase (α-D-glucoside glucohydrolase, EC 3.2.1.20) was isolated fromPenicillium notatum. The enzyme was induced by gibberellic acid (GA3). The GA3-mediated increase in the enzyme activity was repressed in presence of abscisic acid, cycloheximide and the antibiotics chloramphenicol, cordycepin, and rifampicin which are inhibitors of protein synthesis. α-Glucosidase was purified 440-fold with of 27.8-fold of purification. The enzyme was immobilized using chitosan gel. The optimal pH values were 6.5 and 7.5 for free and the immobilized enzymes, respectively. The optimal temperatures were 50 and 65 °C for free and immobilized enzymes, respectively. The enzyme hydrolyzed maltose, sucrose, isomaltose, maltotriose but not starch, amylopectin and amylose. Trehalose and glycerol protected the free and immobilized enzymes against inactivation at 70 °C, however trehalose was the better protector. Phytate protected the free enzyme against heat inactivation at both 65 and 70 °C. 2,4,6 Trinitrobenzenesulfonic acid, butanedione and diethylpyrocarbonate inactivated the enzyme and suggest that, lysyl, arginyl and histidyl groups are taking part in enzyme catalysis. The inactivation by the three compounds was protected by the substratepara-nitrophenyl-α-D-glucopyranoside. Treatment of the enzyme with 1-ethyl-3(3-dimethyl aminopropyl)-carbodiimide,p-chloromercuribenzoate, N-bromosuccinimide, N-acetlyimidazole revealing the involving of carboxyl, sulfhydryl, trptophenyl and tyrosyl groups, respectively in the catalysis of α-glucosidase. EDTA,o-phenanthroline, dipyridyl and 8-quinolinol inhibited the enzyme activity and the inhibition was higher in case of free enzyme compared with immobilized enzyme.