Purification and characterization of sago starch-degrading glucoamylase from Acremonium sp. endophytic fungus

A novel sago starch degrading glucoamylase which had a strong amylopectin-hydrolyzing-activity was purified to homogeneity from a culture filtrate of Acremonium sp. isolated from forest trees. The purified enzyme was an oligomeric protein of two sub-units with molecular weights of 22 and 39 kDa. Optimum temperature and pH for enzyme activity were around 55°C and 5.5, respectively. The enzyme was stable in a pH range of 3.0–7.0 and temperatures up to 60°C. The purified enzyme was strongly inhibited by EDTA. The enzyme catalyzed hydrolysis of amylose and amylopectin, showed apparent Km values of 10.0 and 3.8 mg/ml and Vmax of 195 μmol/ml/min and 391 μmol/ml/min, respectively. Glucose was the sole product released by the hydrolysis, indicating that this enzyme displays an exo-action of starch-degrading activity.