Abstract:An acidic glucoamylase producing strain Aspergillus niger ASP-S21 was isolated from soil. Glucoamylase was purified to homogeneity by ammonium sulfate precipitation ,ion-exchange chromatography with a Sepharose HP column ,and column chromatography with a Sephacryl S-200 column, the molecular weight of SDS-PAGE was 120 kDa. The study of its enzymatic properties showed that the optimum temperature and pH for glucoamylase of such strain were 65 ℃ and 4.0, respectively. Besides, it had good acid stability within the range of pH value from 2.2 to7.6. The Km for glucoamylase was calculated to be 0.94 mg/mL，and the Vmax was 142.43 mol(Glu)/min?L. The enzyme activity was enhanced by Cu2+ and Co2+, and the 10 mM of Cu2+ could improve the glucoamylase activity to 129%. However, the enzyme was strongly inhibited by Fe3+. Its RSGA activities were 0.39U and the RDA values were 4.57%. The glucoamylase was suitable for applying in starch sugar industry.
