Preparation and characterization of a thermostable enzyme (Mn-SOD) immobilized on supermagnetic nanoparticles.

Superoxide dismutase (SOD) has been widely applied in medical treatments, cosmetic, food, agriculture, and chemical industries. In industry, the immobilization of enzymes can offer better stability, feasible continuous operations, easy separation and reusing, and significant decrease of the operation costs. However, little attention has focused on the immobilization of the SOD, as well as the immobilization of thermostable enzymes. In this study, the recombinant thermostable manganese superoxide dismutase (Mn-SOD) of Thermus thermophilus wl was purified and covalently immobilized onto supermagnetic 3-APTES-modified Fe(3)O(4)@SiO(2) nanoparticles using glutaraldehyde method to prepare the Mn-SOD bound magnetic nanoparticles. The Mn-SOD nanoparticles were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer analysis. The results indicated that the diameter of Mn-SOD nanoparticles was 40 (± 5) nm, and its saturation magnetization value was 27.9 emu/g without remanence or coercivity. By comparison with the free Mn-SOD, it was found that the immobilized Mn-SOD on nanoparticles exhibited better resistance to temperature, pH, metal ions, enzyme inhibitors, and detergents. The results showed that the immobilized Mn-SOD on nanoparticles could be reused ten times without significant decrease of enzymatic activity. Therefore, our study presented a novel strategy for the immobilization of thermostable Mn-SOD and for the application of thermostable enzymes.