Purification and characterisation of exo- and endo-inulinase from Aspergillus ficuum JNSP5-06

Three exoinulinases (Exo-I, Exo-II, and Exo-III) and two endoinulinases (Endo-I and Endo-II) were purified from the culture broth of Aspergillus ficuum JNSP5-06 by ammonium sulphate precipitation, DEAE-cellulose column chromatography, Sepharose CL-6B column chromatography and preparative electrophoresis. The molecular weights of Exo-I, Exo-II, Exo-III, Endo-I, and Endo-II were determined to be 70 kDa, 40 kDa, 46 kDa, 34 kDa, and 31 kDa, respectively. Using inulin as the substrate, their Km values were 43.1 mg/ml, 31.5 mg/ml, 25.3 mg/ml, 14.8 mg/ml, and 25.6 mg/ml, respectively. These five inulinases were stable below 50 °C with optimum activity at 45 °C, and were stable at a pH range of 4–8 with an optimum pH at 4.5 for exoinulinase and at 5.0 for endoinulinase. The inulinase activity was completely inhibited by Ag+ and strongly inhibited by Fe2+ and Al3+, whereas K+, Ca2+, Li2+, EDTA and urea had no significant influence on the inulinase activity.