Activity and stability of immobilized alpha-amylase produced by Bacillus acidocaldarius

Abstract

An isolated strain (from rice), Bacillus acidocaldarius was able to produce extracellular α-amylase.The enzyme was partially purified with 50% acetone and showed 4.3-fold purification. Amylase was immobilized on different carriers by different methods and its specific activity for starch hydrolysis studied. Immobilized α -amylase on glass beads (covalent binding) and cation exchange resin (ionic binding) had the highest immobilization yield (85.6 and 84.3%), respectively. It was further observed that, thermal and pH stabilities of immobilized enzymes were higher compared to free enzyme. The immobilized enzymes had higher K (Michaelis constant) and lower V (Maximum A rate of reaction) than the free enzyme. Activation energy (E ) of free enzyme was 2.37 Kcal/mol which was higher than the immobilized enzyme by covalent binding or by ionic binding (1.05 and  1/2 1.59 Kcal/mol), respectively. Half life time (t ) of immobilized enzyme on glass beads was 83 min which was higher than that of immobilized enzyme on cation exchange resin (61 min). Immobilized enzyme on glass beads showed the highest operational stability for up to 8 reuses with 70% residual activity. On the other hand, α-amylase immobilized on cation exchange resin retained 66.2% of its original activity after 8 cycles.