Background: Iron magnetic nanoparticles have attracted much attention.
They have been used in enzyme immobilization because of their
properties such as product is easily separated from the medium by
magnetic separation. The present work was designed to immobilize
horseradish peroxidase on Fe3O4 magnetic nanopraticles without
modification. Results: In the present study, horseradish peroxidase
(HRP) was immobilized on non-modified Fe3O4 magnetic nanoparticles. The
immobilized HRP was characterized by FT-IR spectroscopy, scanning
electron microscopy, and energy dispersive X-ray. In addition, it
retained 55% of its initial activity after 10 reuses. The optimal pH
shifted from 7.0 for soluble HRP to 7.5 for the immobilized HRP, and
the optimal temperature shifted from 40\ub0C to 50\ub0C. The
immobilized HRP is more thermostable than soluble HRP. Various
substrates were oxidized by the immobilized HRP with higher
efficiencies than by soluble HRP. Km values of the soluble and
immobilized HRP were 31 and 45 mM for guaiacol and 5.0 and 7.0 mM for
H2O2, respectively. The effect of metals on soluble and immobilized HRP
was studied. Moreover, the immobilized HRP was more stable against high
concentrations of urea, Triton X-100, and isopropanol. Conclusions:
Physical immobilization of HRP on iron magnetic nanoparticles improved
the stability toward the denaturation induced by pH, heat, metal ions,
urea, detergent, and water-miscible organic solvent