الفهرس 
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Abstract
The study aimed to production of fungal dextranase through biodegradation of dextran using some local isolates of fungi and studying different culture conditions affecting dextranase production. It also aimed to studying physiochemical and kinetic properties of dextranase and improvement of enzyme stability by immobilization and studying the physiochemical and kinetic properties of immobilized dextranase. Eleven fungal strains able to produce dextranase were isolated from some local soil samples. Aspergillus subolivaceus, Aspergillus terreus and Pythium sp. were found to be the most potent dextranase producers. Maximal dextranase productivity was attained at pH 5.5 and 30°C with dextran as carbon source and (NH4)2H2PO4 as nitrogen source. Physiochemical and kinetic properties of dextranase produced from Aspergillus subolivaceus and Aspergillus terreus were investigated and have been found to be; the optimum incubation period was after 20 min and optimum temperature was 60°C for maximum dextranase production. Dextranase showed thermal stability up to 70°C as determination of T1/2 at 50°C, 60°C, 70°C and 80°C. Dextranase also showed storage stability at the end of storage period of 12 weeks and six time thawing. Also kinetic parameters Km and Vmax were determined. Immobilization of dextranase on BSA with covalent binding was studied. And physiochemical and kinetic parameters of Aspergillus subolivaceus immobilized dextranase were investigated and showed that immobilized was most stable than free dextranase. Km and Vmax for immobilized dextranase was less than that for free dextranase. 1-