Immobilization of lysozyme on poly(N-isopropyl acrylamide)/2-hydroxyethyl methacrylate copolymer core–shell gel beads

The immobilization of chicken egg white lysozyme (Lyz) molecules on poly(N-isopropyl acrylamide) gel beads containing 2-hydroxyethyl methacrylate (HEMA) (PGBH) was studied as a function of temperature and HEMA content. Using dynamic and static light scattering measurements, nanometer-sized PGBH particles were shown to exhibit thermo-responsive behavior, and aggregate formation occurred during temperature changes from 25 to 40 °C. The radii of PGBH and Lyz-immobilizing PGBH, the amount of immobilized Lyz and the activity of immobilized Lyz depended on both HEMA content and temperature. Moreover, the activity of immobilized Lyz also depended on the molecular size of the substrates, and the Lyz immobilized on PGBH particles with higher HEMA content showed activity toward low molecular weight substrates at 40 °C nearly equal to that of native Lyz, which indicates that no conformational change in the Lyz molecule occurred after immobilization. These results demonstrate that changes in the activity of the immobilized Lyz were due to a balance of an increase in the affinity between the substrate and Lyz resulting from concentration effects and the steric hindrance between the substrate and Lyz incorporated into the PGBH aggregates with increasing HEMA content and temperature. Furthermore, these results demonstrate that PGBH is a useful material as an enzyme immobilization carrier.