Occurrence of Two Forms of Extracellular Endoinulinase from Aspergillus niger Mutant 817

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Aspergillus niger mutant 817 was generated from A. niger 12,a strain that produces high levels of inulinases irrespective of the carbon source, by γ-irradiation with ^<60>Co. A niger 817 showed 4-fold higher inulinase activity than the wild-type strain 12 in the filtrate of a submerged culture with fructose. An extremely high ratio of inulinase to invertase activity (I/S ratio) of 880 was found in the culture filtrate. Two inulinases, P-IA and P-IB, were purified from the culture filtrate of A. niger 817 grown on sucrose by DEAE-Cellulofine A-500 and Q-Sepharose HP chromatographies. The enzyme were homogeneous as judged by SDS-polyacrylamide gel electrophoresis with apparent molecular weight of 70,000 for P-IA and 68,000 for P-IB. The specific activities were 350 U/mg for P-IA an 340 U/mg for P-IB, and about 3.5-fold higher than that reported for the wild-type endoinulinase P-III. The enzymes were active only toward inulin, and lacked activity toward sucrose, raffinose or levan. The main products of inulin hydrolysis were inulotriose and -tetraose. Thus, both inulinases exhibited the endo-type mode of action on inulin. The apparent K_m values for inulin were 0,48mM for P-IA and 0.5mM for P-IB at 40℃ and pH5.0,and lower than the 1.25mM reported for the wild-type endoinulinase P-III.
社団法人日本生物工学会の論文
1994-08-25