Magnetic microspheres with polymer brushes containing epoxide and amino groups were prepared and used as the support for immobilization of penicillin G acylase.The introduction of the amino group would accelerate the adsorption of enzyme to the support by ionic interaction

and then the adsorbed enzyme was immobilized covalently by reacting with the epoxide group.Magnetic microspheres with atom transfer radical polymerization (ATRP) initiators were first prepared from crosslinked poly(acrylic acid) microspheres in which superparamagnetic Fe3O4 nanoparticles were dispersed.Random copolymer P(GMMA-r-DMAEMA-r-GMA) (GMMA

glycerol monomethacrylate

DMAEMA

N

N-dimethylamino)ethyl methacrylate

GMA

glycidyl methacrylate) was grafted onto the magnetic microspheres by ATRP initiated from the magnetic microsphere initiators.For comparison

magnetic microspheres with P(GMMA-r-DMAEMA) or P(GMMA-r-GMA) brushes were also prepared.The GMMA units in the brushes made the brushes to be hydrophilic; DMAEMA units introduced amine groups and GMA units introduced epoxide groups.Immobilization of penicillin G acylase on these brush-grafted magnetic microspheres showed that both of the activity and activity yield of immobilized penicillin G acylase on P(GMMA-r-DMAEMA-r-GMA) brush-grafted magnetic microspheres were the highest

and the immobilization on them was faster than that on P(GMMA-r-GMA) brushgrafted magnetic microspheres.The immobilized enzyme possessed much higher thermal stability than the free enzyme.The optimal pH value for the immobilized enzyme was slightly higher.After ten cycles of repeated use

70% of the activity still remained.