Dextranase from Penicillium sp. SMCU 3-14 was immobilized on 16-20 mesh sand surface using glutaraldehyde as bifunctional agent. The optimum conditions for the preparation of immobilized dextranase were with 2.5% by volume of glutaraldehyde and the maximal enzyme loading on sand was 0.1690 mg. per gram sand (dry weight). Immobilization was performed at room temperature with agitation speed of 200 rpm. Times and pH for cross-linking and enzyme immobilizing steps were 120 mins at pH 7.0 and 45 mins at pH 4.0, respectively. In comparison to free dextranase, the immobilized dextranase retained 37% of its original specific activity. The optimum pH of the immobilized enzyme was found shift from pH 4.5 to 5.0, while the optimum temperature of both free and immobilized enzyme was found to be the same at 55 ํC. As of pH stability, immobilized dextranase was stable within a narrow pH range, between 3.5 to 5.5, whereas its temperature stability was better than of the free enzyme. Moreover, the immobilized enzyme could retain more than 95% of its activity even stored for 30 days in 0.05 M acetate buffer pH 4.5 at 4 ํC. After the tenth cycle of its repetative hydrolysis, the enzyme still gave 65% of its initial activity. Finally, the Michaelis constant, Km of the immobilized dextranase toward its substrate dextran T-2000 was 12.50 mu M, which is higher than that of free enzyme.
