ABSTRACT
ALPHA-AMYLASE 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 a amylase exhibited a higher K[m] [Michaelis constant], lower V[max] [maximal reaction rate] and lower E[A] [activation energy] than the native enzyme. Covalent attachment of alpha- 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 t[1/2] [half-life time] values of heat inactivation energy at 50, 60°C were 89 and 56 mm, respectively for the conjugated enzyme, whereas at these temperatures the native enzyme was less stable [t[1/2] 60 and 47 min, respectively]. The deactivation rate constant at 80°C for the conjugated a-amylase is about 11.9x10[-3]/ min, which is lower than that of the native enzyme [14.8x10[-3]/ min]. Conjugated a-amylase was more stable against chemical denaturation than the native enzyme, and retained 70.6% of its activity in presence of CuSO[4] [10 mM] while the native form of retained only 34.1%