Enzymatic synthesis of S-bzl-γ-Glutamyl-L-Cysteine with γ-glutamyltranspeptidase immobilized onto ordered mesoporous TiO₂

γ-Glutamyltranspeptidase (GGT) was adsorbed from B. subtilis NX-2 onto ordered mesoporous TiO₂ (OM-TiO₂). The immobilized GGT was characterized with circular dichroism spectrum and active site titration method. The secondary structure and number of active sites of GGT were little affected after immobilization. The immobilized GGT appeared some decline in the affinity of GGT toward donor substrate and catalytic constants. However, the affinity of immobilized GGT toward S-bzl-GGC was much higher than that of free GGT. Thermal and pH stability of GGT were significantly increased via immobilization. Residual activity of immobilized GGT still exceeded 74% of its initial value after reusing for 10 batches. At the conditions of Gln 5 mmol/L, S-bzl-cys 15 mmol/L, immobilized GGT 0.062 U/mL and pH 9.0, a maximal product yield of 1.2 mmol/L was obtained after incubation at 40°C for 5 h.