Lactam-amide graft copolymers as novel support for enzyme immobilization

A graft random copolymer of N-vinyl-2-pyrrolidone and N,N'-dimethylacrylamide onto polypropylene was synthesized using a simultaneous gamma radiation technique from a Co-60 source, so that the hydrogel poly(propylene-g-vinylpyrrolidone-co-N,N'-dimethylacrylamide) [PP-g-(VP-co-DMAM)], thus produced by grafting, could be used as a support for enzyme immobilization. The grafted spheres showed very good swelling behavior in water due to the incorporation of hydrophilicity in the PP spheres. The influence of pH and temperature on as well as the determination of the kinetic parameters, K-M and V-max for both immobilized and soluble invertase were determined. PP-g-(VP-co-DMAM) grafting onto the PP spheres caused a significant change in the water content of the support and was more pronounced for the spheres with a high degree of grafting. A porous structure of the polymeric spheres was observed by scanning electron microscopy (SEM). The porous structure contributed to the reaction rate decrease due to diffusional effects, as shown by the larger K-M value observed for immobilized invertase relative to the free enzyme. The enzyme affinity for the substrate (K-M/V-max) remains quite good after immobilization. The thermal stability of immobilized invertase was significatively higher than that of the free enzyme and a displacement of 20degreesC was observed for the immobilized enzyme. (C) 2002 John Wiley Sons, Inc.