Purification and thermodynamic characterization of glucose oxidase from a newly isolated strain of Aspergillus niger

An intracellular glucose oxidase (GOD) was isolated from the mycelium extract of a locally isolated strain of Aspergillus niger NFCCP. The enzyme was partially purified to a yield of 28.43% and specific activity of 135 U mg(-1) through ammonium sulfate precipitation, anion-exchange chromatography, and gel filtration. The enzyme showed high specificity for D-glucose, with a K(m) value of 25 mmol L(-1). The enzyme exhibited optimum catalytic activity at pH 5.5. Optimum temperature for GOD-catalyzed D-glucose oxidation was 40 degrees C. The enzyme displayed a high thermostability having a half-life (t(1/2)) of 30 min, enthalpy of denaturation (H*) of 99.66 kJ mol(-1), and free energy of denaturation (G*) of 103.63 kJ mol(-1). These characteristics suggest that GOD from A. niger NFCCP can be used as an analytical reagent and in the design of biosensors for clinical, biochemical, and diagnostic assays.