Partial Purification and Characterization of a Thermostable β-Mannanase from Aspergillus foetidus

An extracellular beta-mannanase was isolated from samples of crude extract of the mesophilic fungus Aspergillus foetidus grown on soybean husk as a carbon source. The induction profile showed that beta-mannanase reached a maximum activity level (2.0 IU/mL) on the 15th day of cultivation. The enzyme was partially purified by ultrafiltration and gel filtration chromatography procedures and was named Man 58. Sodium dodecyl sulfate-polyacrilamide electrophoresis and zymogram analysis of Man 58 showed two bands of approximately 43 and 45 kDa with beta-mannanase activity. Ultrafiltration showed that beta-mannanase activity was only detected in the concentrated sample. Man 58 was most active at 60 degrees C and at pH 4.0. It was thermostable in the temperature range of 40-60 degrees C for eleven days, and the half-life at 70 degrees C was ten days. Man 58 showed K-m and V-max values of 3.29 mg/mL and 1.76 IU/mL respectively, with locust bean gum as a substrate. It was mostly activated by FeSO4 and CoCl2 and inhibited by MgSO4, FeCl3, CuSO4, MgCl2, ZnCl2, ZnSO4, CaCl2, CuCl2, KCl and ethylenediaminetetraacetic acid (EDTA). Phenolic compounds did not inhibit the enzyme. On the other hand, auto-hydrolysis liquor showed an inhibitory effect on Man 58 activity.