A new metal-chelated beads for reversible use in uricase adsorption

Poly(ethylene glycol dimethacrylate-n-vinyl imidazole) [poly(EGDMA-VIM)] beads (average diameter 150–200 μm) was prepared by copolymerizing ethylene glycol dimethacrylate (EGDMA) with n-vinyl imidazole (VIM). Average pore size of poly(EGDMA-VIM) beads was 550 nm. The copolymer beads composition was characterized by elemental analysis and found to contain five EGDMA monomer units each VIM monomer unit. Poly(EGDMA-VIM) beads had a specific surface area of 59.8 m2/g. Poly-(EGDMA-VIM) beads were characterized by swelling studies and SEM. Cu2+ ions were chelated on the poly(EGDMA-VIM) beads, then these beads were used in the adsorption of uricase from Porcine Liver in batch system. The maximum uricase adsorption capacity of the poly(EGDMA-VIM)-Cu2+ beads was observed as 118.3 mg/g at pH 6.0. The Km values for immobilized uricase (poly(EGDMA-VIM)-Cu2+) (91.95 × 10−3 mM) was higher than that of free enzyme (7.5 × 10−3 mM). Vmax was calculated as 0.012 μmol/min mg protein for the free enzyme. For the immobilized enzyme, Vmax was calculated as 1.44 μmol/min mg protein. Free enzyme lose all of original activity in 35 days. On the other hand immobilized enzyme preserved 80% of original activity in same time. 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.