Immobilization of β-glucosidase on mercaptopropyl-functionalized mesoporous titanium dioxide

Mesoporous titanium dioxide (M-TiO2) and mercaptopropyl-functionalized M-TiO2 (SH-M-TiO2) were prepared as carriers for immobilization of β-glucosidase (BG). Analyses suggested that in SH-M-TiO2 the grafted mercaptopropyl groups attributed to about 3.5% of the total weight of the matrices. For the immobilization of BG, SH-M-TiO2 or M-TiO2 powder was added with free BG solution and stirred at 4 °C for 8 h, followed by centrifugation and washing. BG was effectively immobilized on SH-M-TiO2 with an enzyme activity of 10.9 U/g, which was 92.8% of the total enzyme activity in the starting solution of free BG. BG immobilized on SH-M-TiO2 (BG-SH-M-TiO2) was more stable in pH, thermal, and storage tests than BG on M-TiO2 or free BG in solution. The Km and vmax of BG-SH-M-TiO2 were similar to values for free BG in solution. Batch hydrolysis of cellobiose-containing substrate by BG-SH-M-TiO2 was conducted. Conversion rates of cellobiose in 10 batches were consistently around 90%. Although the residual enzyme activity of BG-SH-M-TiO2 decreased gradually, only a small amount of BG activity was detected in supernatants. This indicated effective adsorption of enzyme molecules to SH-M-TiO2 matrices.