Immobilization of GGT on meso-TiO₂: preparation and properties

γ-Glutamyltranspeptidase (GGT) is an important enzyme with wide applications in biocatalysis and clinical diagnosis. In this work, mesoporous fibrous titania (M-TiO₂) was used for immobilization of GGT from B. subtilis NX-2 and the properties of immobilized GGT were also investigated. When the M-TiO₂ support with average pore diameter of 30 nm was used, the amount of immobilized protein was 5.07 mg · g^-1, and the yield of activity was 73.05% at the ratio of GGT/support was 18.99 U · g^-1 after incubation at room temperature for 2.5 h. The thermal and pH stability of the immobilized GGT was higher than that in its free form. After storage at 4°C for 60 days and repeated use for 22 batches, the activity of the immobilized GGT remained 71.30% of its initial activity. The kinetic parameters (K_m) for free and immobilized GGT were determined as 0.79 mmol · L^-1 and 1.05 mmol · L^-1, respectively. The activation energy (E_a) values of glutamylation were 15.42 kJ · mol^-1and 13.59 kJ · mol^-1 for immobilized and free GGT. The thermal inactivation energy (E_d) values of GGT for immobilized and free enzyme were also calculated to be 92.80 kJ · mol^-1 and 49.61 kJ · mol^-1, respectively.