Simple and efficient procedures were developed to prepare the
carboxyl functioned magnetic Fe3O4 nanoparticles for the immobilization
of glucoamylase by direct bonding. The immobilized
glucoamylase shows different activity in wider ranges of temperature
and pH, compared with its free form. In addition, the
immobilized enzyme could be stored for 25 days with 70% activity
maintenance. Kinetics analysis shows that the immobilized enzyme
had a lower affinity for binding substrate than free enzyme. Furthermore,
the immobilized enzyme could accomplish utilization
successively but the residual activity was about 40% of its initial
activity after 8 cycles.