Novel metal-chelate affinity sorbents for reversible use in catalase adsorption

A novel metal-chelate adsorbent utilizing N-methacryloyl-(L)-histidine methyl ester (MAH) as a metal-chelating ligand was prepared. MAH was synthesized by using methacryloyl chloride and L-histidine methyl ester dihydrochloride. Magnetic beads with an average size of 150-250μm were obtained by suspension polymerization of ethylene glycol dimethacrylate (EGDMA), and MAH conducted in aqueous dispersion medium. The specific surface area of the porous beads was found to be 80.1m²/g. Mag-poly(EGDMA-MAH) beads were characterized by swelling tests, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). Elemental analysis of MAH for nitrogen was estimated as 43.9μmol/g. Then, Fe ³⁺ ions were chelated on the magnetic beads. Fe³⁺- chelated magnetic beads with a swelling ratio of 40% were used in the adsorption of catalase in batch system. The maximum catalase adsorption capacity of the mag-poly(EGDMA-MAH)-Fe³⁺ beads was observed as 83.2mg/g at pH 7.0. The K_m values for immobilized catalase (mag-poly(EGDMA-MAH)-Fe³⁺) (20.5mM) were higher than that of free enzyme (16.5mM). Storage stability was found to increase with immobilization. It was observed that enzyme could be repeatedly adsorbed and desorbed without significant loss in adsorption capacity or enzyme activity.