Purification and characterization of extracellular glutaminase from Aspergillus oryzae NRRL 32567

The glutaminase produced from Aspergillus oryzae NRRL 32567 was purified (10.2 folds) using ammonium sulfate fractionation followed by gel filtration on Sephadex G-75. SDS-PAGE of the purified glutaminase showed the presence of one band with a molecular weight of 68 kDa. Optimum pH was 7.0 while a temperature range 30–40 °C was optimal the activity. The highest pH stability was obtained at pH 7.0 while a temperature range 30–40 °C resulted in the highest temperature stability. The apparent Km value was calculated from the Linenweaver-Burk plot and was found to be 4.5 mM. Glutamine was the preferred substrate for the enzyme and the maximum relative activity of 130% was observed at 2.5% glutamine . Potassium showed a slight increase in activity of glutaminase especially at the concentration of 0.5 mM. While, frerric ions followed by ferrous showed the highest inhibition effect on glutaminase.