Effect of Divalent Metal Ions on Glucoamylase Activity of Glucoamylase Isolated from Aspergillus niger

This study investigates the production of glucoamylase from Aspergillus niger in a submerged fermentation process using amylopectin fractionated from guinea corn starch as the carbon source. This work also studies the effect of a few metal ions (Ca2+, Zn2+, Co2+, Fe2+, Mn2+ and Pb2+) concentration on the glucoamylase activity. A Fourteen day experimental study was carried out to determine the day of highest glucoamylase activity. Maximum glucoamylase activity was observed on day five of the submerged fermentation; hence, day five was mass produced. The specific activity for the crude enzyme was found to be 729.45 U/mg. The crude enzyme was purified to the level of gel filtration (using sephadex G-100) via ammonium sulphate precipitation. Ammonium sulphate saturation of 70% was found suitable to precipitate the enzyme. After ammonium sulphate precipitation and gel filtration, the specific activities were found to be 65.98 U/mg and 180.52 U/mg respectively. The glucoamylase activity was enhanced by 2 mM to 5 mM of Ca2+, Co2+, Fe2+, Mn2+and Zn2+ but Pb2+ had inhibitory effect on the enzyme. The Michaelis constant, Km and maximum velocity Vmax of the enzyme was obtained from the Lineweaver-Burk plot of initial velocity data at different substrate concentrations. They were found to be 770.75 mg/ml and 2500 μmol/min respectively, when using cassava starch as substrate. The enzyme glucoamylase is known to have useful applications in food processing industries and fermentation biotechnology