抄録
Expanded poly(tetrafluoroethylene) (ePTFE) films grafted with 2-hydroxyethyl methacrylate (HEMA) were applied to a polymer support for urease immobilization. The amount of absorbed water for HEMA-grafted ePTFE (ePTFE-g-PHEMA) films prepared by the combined use of the plasma treatment and photografting increased with an increase in the grafted amount and the ePTFE-g-PHEMA films possessed high water-absorptivities. Imidazole groups were introduced to grafted PHEMA chains with 1, 1′-carbonyldiimidazole in acetonitrile, and then urease was covalently immobilized to the ePTFE-g-PHEMA films in a pH 7.0 buffer at 4°C. The activity of urease immobilized at pH 7.0 had the maximum value at the optimum pH level of 7.5 for native urease. The relative activity of immobilized urease was kept almost constant in the range below the immobilized amount of 40mg/g-ePTFE and decreased probably due to crowding of urease molecules in the grafted layers at further increased immobilized amounts. An increase in the grafted amount resulted in a decrease in the relative activity of immobilized urease because the diffusivity of the substrate urea into the grafted layer decreased. The optimum temperature of the activity for urease was shifted to 60°C from 30°C for native urease by the covalent immobilization onto the ePTFE-g-PHEMA films and immobilized urease was repeatedly usable without a considerable decrease in the activity in the regions of the pH 6.0 to 9.0 and 10 to 60°C.
