Catalase immobilization on amino-activated Fe3O4@SiO2 nanoparticles: Loading density affected activity recovery of catalase

A blackberry-shaped Fe₃O₄@SiO₂ nanoparticles were prepared, characterized and applied in covalently binding catalase. The enzyme loading decreased with the increase of pH, however, the activity recovery increased simultaneously. To elucidate the influence factor of the activity recovery, the enzyme loading was further regulated by changing the initial free enzyme content. The relationship between enzyme loading and activity recovery showed the consistent trend, whether the variation of enzyme loading was incurred by pH or by initial enzyme content. The simulated parameters showed the similar values according to the experiment at different conditions. It was concluded that activity recovery was dominated by protein density on surface, not by the orientation of the enzyme on surface, due to the negligible diffusion limit for H₂O₂ as the substrate of catalase. The immobilized catalase at pH 7.0 has a high activity recovery of 100% at 14.4 enzyme μg/mg nanoparticles. The K_m and V_max of the immobilized enzyme above are 0.215 mol and 0.797 mol/min, similar to 0.167 mol and 0.727 mol/min for the free enzyme, respectively.