Immobilization of Laccase on SiO2 Nanocarriers Improves Its Stability and Reusability

Laccases have a broad range of industrial applications. In this study, we immobilized laccase on SiO2 nanoparticles to overcome problems associated with stability and reusability of the free enzyme. Among different reagents used to functionally activate the nanoparticles, glutaraldehyde was found to be the most effective for immobilization. Optimization of the immobilization pH, temperature, enzyme loading, and incubation period led to a maximum immobilization yield of 75.8% and an immobilization efficiency of 92.9%. The optimum pH and temperature for immobilized laccase were 3.5 and 45 degrees C, respectively, which differed from the values of pH 3.0 and 40 degrees C obtained for the free enzyme. Immobilized laccase retained high residual activities over a broad range of pH and temperature. The kinetic parameter V-max was slightly reduced from 1,890 to 1,630 mu mol/min/mg protein, and K-m was increased from 29.3 to 45.6. The thermal stability of immobilized laccase was significantly higher than that of the free enzyme, with a half-life 11- and 18-fold higher at temperatures of 50 degrees C and 60 degrees C, respectively. In addition, residual activity was 82.6% after 10 cycles of use. Thus, laccase immobilized on SiO2 nanoparticles functionally activated with glutaraldehyde has broad pH and temperature ranges, thermostability, and high reusability compared with the free enzyme. It constitutes a notably efficient system for biotechnological applications.