Vinyl imidazole carrying metal-chelated beads for reversible use in yeast invertase adsorption

Poly(ethylene glycol dimethacrylate-n-vinyl imidazole) [poly(EGDMA-VIM)] hydrogel (average diameter 150-200 μm) was prepared copolymerizing ethylene glycol dimethacrylate (EGDMA) with n-vinyl imidazole (VIM). Poly(EGDMA-VIM) beads had a specific surface area of 59.8 m2/g. Poly(EGDMA-VIM) beads were characterized by swelling studies and scanning electron microscope (SEM). Cu2+ ions were chelated on the poly(EGDMA-VIM) beads (452 μmol Cu2+/g), then the metal-chelated beads were used in the adsorption of yeast invertase in a batch system. The maximum invertase adsorption capacity of the poly(EGDMA-VIM)-Cu2+ beads was observed as 35.2 mg/g at pH 4.5. The adsorption isotherm of the poly(EGDMA-VIM)-Cu2+ beads can be well fitted to the Langmuir model. Adsorption kinetics data were tested using pseudo-first- and -second-order models. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The value of the Michaelis constant Km of invertase was significantly larger upon adsorption, indicating decreased affinity by the enzyme for its substrate, whereas Vmax was smaller for the adsorbed invertase. The optimum temperature for the adsorbed preparation of poly(EGDMA-VIM)-Cu2+-invertase at 50 °C, 10 °C higher than that of the free enzyme at 40 °C. Storage stability was found to increase with adsorption. Adsorbed invertase retains an activity of 82% after 10 batch successive reactions, demonstrating the usefulness of the enzyme-loaded beads in biocatalytic applications.