Abstract

In this present study, extracellular glucoamylase was secreted from Aspergillus flavus an organism isolated from cassava flour and identified with the feature of the strain. The crude enzyme was precipitated at 80 % ammonium-sulphate, followed by ion-exchange chromatography on carboxyl-methylSephadex C-25, affinity chromatography on sepharose 4B and gel-filtration on sephacryl S-200. The peak with the highest activity was pooled from latter chromatographic step and characterized afterwards. The specific activity of the purified enzyme was approximately 0.59 to 7U/mg of protein with a yield of 11.58 % and 22.1 purification fold. The optimal pH and temperature of the enzyme were 7.0 and 50 0 C respectively. The enzyme was observed to be thermostable at the 50 0 C for 15 to 30 mins. The kinetic parameters Km and Vmax for the enzyme were 0.934 mg/ml and 6.452U/min respectively. The effect of selected cations and chemical compounds at concentrations of 1 mM, 5 mM and10 mM revealed the activating effect of Ca 2+ while Al 3+ , Cu 2+, Mg 2+ , K + , Na + , EDTA, mercaptoethanol and urea inhibit the enzyme’s activity. The apparent molecular weight of the enzyme as determined by gel filtration on sephacryl S-200 was 28 KDa while the subunit molecular weight as determined on SDS PAGE was approximately 25 KDa.