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Pakistan Journal of Biological Sciences
Year: 2002  |  Volume: 5  |  Issue: 5  |  Page No.: 589 - 593

Some Properties of Inulinase from Aspergillus fumigatus

Mona K. Gouda    

Abstract: A local isolate identified as Aspergillus fumigatus was tested for inulinase and invertase production. Different carbon sources alone or in combination with inulin were tested. About 91% inulinase was found as extracellular enzyme in culture medium with inulin and wheat bran as sole C-source (1% for each). The activity towards sucrose (invertase enzyme) was detected only in the supernatant and represents about 26% from the inulinase activity. The production of both enzymes was inhibited with ammonical compounds as nitrogen source, whereas the maximum level (3.72, 0.35 U/ml for inulinase and invertase respectively) was observed when 0.38% KNO3 was used as nitrogen source. Beef extract, yeast extract, peptone and tryptone reduced the amount of inulinase by about 83-91%. Both enzymes were produced in a broad pH range between 4.0-8.0 as initial pH. Optimum temperature was found to be 30°C for inulinase and a dramatic reduction was observed above 35°C, while 40°C was observed for invertase. The properties of crude inulinase were also studied. The enzyme has optimum pH 5.5 in acetate buffer and optimum temperature 45°C. Fructose at concentrations higher than 0.2mg/reaction mixture inhibited the enzyme activity. The enzyme was stable for 30 min at 30°C and 40°C in pH 5.5 and for 24h at 4°C in pH 6 - 6.5. Addition of 10% glycerol protected the enzyme from deactivation at 45°C and 50°C for 30 min. The enzyme was completely inhibited by 1mM Ag+ and Hg2+ and activated by the presence of 1mM Ca2+ or Mn2+.

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