Glucose oxidase from Aspergillus niger: Production, characterization and immobilization for glucose oxidation

Glucose oxidase (GOx), a flavoenzyme, from Aspergillus niger was produced, purified and immobilized for glucose oxidation. Maximum activities of 0.6 and 0.31U mg fungus dry weight were obtained as intracellular and extracellular respectively. Optimal production (4000 IU/L) was achieved when basal salt medium was supplemented with sucrose (7.5%), peptone (1.5%) phosphorus (0.2%) and MgSO4 (0.2%) at pH 5.7 after 48 h at 250 rev. min . Enzyme purified by ammonium sulphate precipitation (75%), gel filtration, Q-Sepharose and DEAE Sepharoses has 30.08, 63.3% and 22.3 fold purification, % recovery and specific activity respectively. Enzyme was dimeric consisting of two equal subunits with molecular weight of 80 kDa. and displayed temperature and pH optima 2530°C and 5.5-6.0 respectively for the oxidation of-D-glucose. The enzyme was stable at 50 °C for 1 h without any prior stabilisation. Vmax, and Km value 17 Umg -1 and Km, 7.1mM respectively. GOx was inhibited by Cu 2+ (56.5%), and Ag (48%) appreciably and to a lower extent by NaF (25%). Covalent immobilization of enzyme with oxirane beads was less effective and enzyme lost activity, but entrapment methods of sodium alginate and poly acrylamide was effective for the oxidation of glucose.