A HGCL2 INSENSITIVE AND THERMALLY STABLE INULINASE FROM ASPERGILLUS-ORYZAE

An extracellular inulinase (EC 3.2.1.7) from Aspergillus oryzae growin g on inulin-containing medium was purified by CM-cellulose and Sephade x G-200 column chromatographies to electrophoretic homogeneity. The pu rified inulinase cleaved beta-linked fructose from inulin and sucrose with S/I ratio of 2.4. It had a remarkable stability in heat, losing o nly 41 and 32% of its inulin hydrolytic activity after 2 h at 90 degre es and 100 degrees, respectively. The pattern of thermal denaturation of both the inulin and sucrose hydrolytic activities was nearly the sa me. SO42- and Fe3+ were strong inhibitors of inulin and sucrose hydrol ytic activities,whereas Ba2+ was an activator. Hg2+ inhibited sucrose hydrolytic activity but increased inulin hydrolytic activity of inulin ase. It is proposed that inulinase has different sites for binding of sucrose and inulin and these are either very close to or partially ove rlapping. The sulphydryl group is in the non-overlapping zone of the s ucrose binding site and its modification by HgCl2 results in an enhanc ed inulin hydrolytic activity. In the presence of inulin and sucrose t ogether, both substrates compete with each other resulting in reduced activity compared with that observed with individual substrate. Inulin ase had a temperature optima of 55 degrees and a mass of 38 kd. (C) 19 98 Elsevier Science Ltd. All rights reserved.