CATALYTIC PROPERTIES OF IMMOBILIZED TANNASE PRODUCED FROM Aspergillus aculeatus COMPARED WITH THE FREE ENZYME

摘要

Aspergillus aculeatus tannase was immobilized on several carriers by entrapment and covalent binding with cross-linking. Tannase immobilized on gelatin with cross-linking agent showed the highest activity and immobilization yield. The optimum pH of the immobilized enzyme was shifted to a more acidic range compared with the free enzyme (from pH 5.5 to pH 5.0). The optimum temperature of the reaction was determined to be 50°C for the free enzyme and 60°C for the immobilized form. The thermal stability, as well as stability over a wide range of pH, was significantly improved by the immobilization process. The calculated K_m of the immobilized tannase (11.8 mg ml~(-1)) is higher than that of the free tannase (6.5 mg ml~(-1)), while V_(max) of the immobilized enzyme (0.32 U (μg protein)~(-1)) is lower than that of the free tannase (2.7 U (μg protein)~(-1)). The immobilized enzyme was able to retain 84 % of the initial catalytic activity after 5.0 cycles.