PURIFICATION OF AN EXO-INULINASE FROM BACILLUS SP. SG7

Abstract

An exo-inulinase from strain Bacillus sp. SG7 was isolated and purified. A two-phase system PEG/Dextran, size-exclusion chromatography and ion-exchange chromatography were used in the purification process. The enzyme was purified to homogeneity with specific inulinase activity 18.47 U/mg protein and specific invertase activity 196.5 U/mg protein, purification fold of 10.44 and 27.4% yield. The molecular mass of the purified enzyme was estimated to be 56 000 Da. Strong inhibitors of enzyme activity are Pb, Hg, Zn and Cu ions with inhibition levels rising up to 55% for Cu and 95% for Pb. SDS totally inhibited the purified inulinase. The kinetic constants Km and Vmax for inulin as substrate were determined to be 1.0 mg/mL and 6.25 mg/mL.h, respectively. The pH optimum is at pH 7.0 and the enzyme is stable between pH 6.0 and pH 7.5, while retaining 100% of its initial activity between pH 6.5 and pH 7.0. The temperature optimum for the purified inulinase from strain Bacillus sp. SG7 was at 60°С. In the presence of inulin the purified inulinase sustains its activity at 100% for 55 minutes at 65°С. After the 70th minute the residual activity is 63% of the initial. The enzyme showed capacity to hydrolyse sucrose, raffinose and inulin from which it liberated only fructose units showing, therefore, an exo-action mechanism. The inulins from chicory (Cichorium intibus), from dahlia (Dahlia pinnata) and Jerusalem artichoke (Helianthus tuberosus) roots were hydrolysed by the purified enzyme.