Purification and characterization of a thermostable glucoamylase from Aspergillus fumigatus

A thermostable glucoamylase from Aspergillus fumigatus was purified to homogeneiry. It was a glycoprotein with 23% carbohydrate content and an apparent molecular mass of 42 kDa. The enzyme showed maximal activities at pH 4.5-5.5 and 65 degrees C and preferentially attacked polysacharides, such as starch, glycogen, amylopectin, and amylose, rather than maltose and maltoriose. The K-m and V-max of soluble starch hydrolysis at 40 degrees C and pH 5.0 were 0.1 mg.mL(-1) and 161 mu mol glucose equivalents liberated.min(-1).mg protein(-1), respectively. The purified enzyme was remarkably insensitive to glucose. It was not affected by 500 mM D-glucose and retained about 80% of its original activity in the presence of 1000 mM of this sugar.