Biochemical characterization and stability assessment of Rhizopus oryzae lipase covalently immobilized on amino-functionalized magnetic nanoparticles.

Amino-functionalized magnetic nanoparticles (Fe3 O4 ) have been investigated as a support for covalent immobilization of lipase. The nanoparticles were prepared by chemical coprecipitation method and subsequently were coated with 3-aminopropyltriethoxysilane (APTES) via silanization reaction. With glutaraldehyde, as the coupling agent, the lipase from Rhizopus oryzae was successfully immobilized onto the amino-functionalized magnetic nanoparticles. The synthesized support was characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The results showed that the load of immobilized protein could reach as high as 7mg protein g-1 support. The optimum pH for maximal catalytic activity of the immobilized enzyme was 8.0 at 40°C. The Km values were found as 0.66 and 0.57mgmL-1 for the free and immobilized enzymes, respectively. The Vmax values for the free and immobilized enzymes were calculated as 0.14 and 0.47μmolmg-1 min-1 , in turn, when p-nitrophenyl butyrate (pNPB) was used as the substrate. A quick separation of lipase from the reaction mixture was achieved when a magnetically active support was applied. In comparison to the free enzyme, the immobilized enzyme was thermally stable and was reusable for 10 cycles while retaining 64% of its initial activity.