Functional Change of Dextran-modified α-amylase from Bacillus acidocaldarius

αAMYLASE from Bacillus acidocaldarius was modified by covalent coupling to activated dextran with retained activity of 77.7 %. After conjugation, the enzyme was stable within a broader pH range than the native enzyme and its optimum temperature increased by 10C compared to the native enzyme. The conjugated αamylase exhibited a higher Km (Michaelis constant), lower Vmax (maximal reaction rate) and lower EA (activation energy) than the native enzyme. Covalent attachment of - amylase to activated dextran protected the enzyme against heat inactivation. In the presence of the substrate, the conjugated enzyme retained 68.2 % of its original activity after incubation at 70C for 30 min which was more than that retained by the native enzyme (50.3 %) under the same conditions. The calculated t1/2 (half-life time) values of heat inactivation energy at 50, 60 C were 89 and 56 min, respectively for the conjugated enzyme, whereas at these temperatures the native enzyme was less stable (t1/2 60 and 47 min, respectively). The deactivation rate constant at 80 C for the conjugated α-amylase is about 11.9x10-3/ min, which is lower than that of the native enzyme (14.8x10-3/ min). Conjugated α-amylase was more stable against chemical denaturation than the native enzyme, and retained 70.6% of its activity in presence of CuSO4 (10 mM) while the native form of retained only 34.1%