Direct binding glucoamylase onto carboxyl-functioned magnetic nanoparticles

[Display omitted] ► Carboxyl functioned magnetic Fe3O4 nanoparticles (CMNPs) as support. ► The effects of immobilization of condition on the activity of immobilized enzyme were investigated. ► Catalysis characteristics of immobilized glucoamylase were compared with free enzyme. A novel and efficient immobilization of glucoamylase from Aspergillus niger has been developed by using carboxyl functioned magnetic Fe3O4 nanoparticles (CMNPs) as support. The CMNPs were prepared by co-precipitation of Fe2+/Fe3+ with oleic acid as surfactant and consequent oxidation of CC into COOH by KMnO4 solution in situ. And then glucoamylase was directly bonded onto the magnetic nanoparticles. The bonding was verified by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. The immobilization process was investigated by examining immobilization time, enzyme concentration and pH. As a result, it could gain an enzyme loading with 120mg glucoamylase/g magnetic nanoparticles and specific activity of 90U/mg protein while 1mg/mL glucoamylase and 10mg/mL ferrofluid were mixed at pH 6.0 and 25°C for 16h. The immobilized enzyme presented a same or better storage, pH and thermal stability than the free enzyme and could be reused. And the residual activity was about 40% after 8 cycles. The Michaelis constant (Km) showed that affinity of immobilized enzyme for binding substrate was lower than free enzyme.