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Abstract
In the present study, 15 bacterial strains were tested to obtain a potent strain capable to produce a-amylase. Bacillus acidocaldarius was the potent strain so it was used for further study. Some cultural conditions were investigated to improve the productivity of the enzyme by B. acidocaldarius Partial purification of the enzyme was achieved by fractional precipitation of the crude enzyme by organic solvents like, ethanol and acetone and by salt like, ammonium sulfate. The acetone fraction at 50% and ethanol fraction at 60% exhibited the highest recovered activity with the highest specific activity. Acetone fraction at 50% was recommended and it was used for the succeeding study. Some properties of the partially purified enzyme were investigated. Improving of thermal and pH stabilities were conducted by chemical modification of the enzyme by covalent coupling to soluble polysaccharides. The enzyme coupled to activated dextran (MW 70,000) showed the highest retained activity. The properties of the native and conjugated enzyme were compared. The enzyme was immobilized on solid carriers by physical adsorption, entrapment, covalent binding and ionic binding. The immobilized enzyme on cation exchange resin (ionic binding) and glass beads (covalent binding) showed the highest immobilization yield. The properties of the free and immobilized enzyme were compared.