Characterization of Free and Immobilized P.aculeatum NRRL-896 Dextranase

Abstract

The characterization of free and immobilized dextranase on oyster mushroom stem by cross-linking technique with glutaraldehyde were studied. The optimum pH of the immobilized dextranase was shifted to a higher value (5.5) from pH 4.5, which was the optimal for the free enzyme, the immobilized dextranase was significantly stable over wide range of pH (4 to 8.0) than the free enzyme (pH; 4 to 6.5). This result indicated that the immobilized dextranase was more resistant to pH changes and could be used industrially.The optimal reaction temperature of the immobilized dextranase was shifted from 45 °C for the free dextranase to 55 °C and the thermal stability ranged from (35 - 65 °C) compared to (35 - 45 °C) for the free dextranase. This indicated that the immobilization process improved the thermal stability of dextranase relative to free enzyme. Dextranase activity of both free and immobilized enzyme did not change in the present of different sugars (sucrose, glucose, fructose, mixture of (sucrose + glucose + fructose) except that of mannitol and starch were 78.5 and 91.8 % residual activity, respectively. Metals ions (CoCl3, MnCl2, PbCl2, CuCl2, AlCl3 and MgCl2,) tested had no effect on dextranase activity except Fe+2, Fe+3 and Hg+2 had 24.2, 28.1 and 51.8 % residual activity, respectively. However, aluminum chloride had slightly inhibitory effect with 97% residual activity and retained 73.4 % residual activity of the purified dextranase, while with cobalt Co+3 retained 78.5% of dextranase activity. Only Mn+2 and Mg+2 had stimulatory effect on dextranase activity. Linweaver Burk plots showed that Km of the immobilized dextranase was (86.43 ± 0.1 mg mL-1) via glutaraldehyde with appreciably higher values than that the free dextranase (52.13±0.02 mg mL-1). While Vmax (1/slope) of the immobilized enzyme (2.98 ± 0.03 µmole min-1) is equally to the free dextranase (2.97±1.02 µmole min-1).