Covalent immobilization of urease onto modified florisil and characterization of free and immobilized urease

Purpose: In this study, it was aimed to immobilize urease from Canavalia ensiformis onto modified Florisil (magnesium silicate) by covalently and to characterize immobilized urease and also to investigate reusability of immobilized urease in a batch type bioreactor. Materials and Methods: Florisil was activated with 3-aminopropyltriethoxysilane and then modified with glutaraldehyde. Urease was covalently immobilized onto modified support. Images of support and immobilized urease were examined on a scanning electron microscope. The optimum pH and temperature, kinetic parameters (K-m, V-max k(cat)/K-m) and storage stabilities at 4 degrees C and room temperature of free and immobilized ureases were determined. Reusability of immobilized urease was investigated in a batch type bioreactor. Results: Free and immobilized ureases showed their maximum activities at pHs 7.0 and 6.5, and at temperatures 50 and 60 degrees C, respectively. The K m value of immobilized urease increased 2.2 fold compared to free urease. The catalytic efficiency of immobilized urease was about 0.1% of the free urease. Free urease completely lost its activity at the end of 5 days stored at 4 degrees C and room temperature; however, immobilized urease did not lose its activity at the end of 19 days at the same conditions. Immobilized urease maintained 50% of its initial activity at the end of 10 reuses in batch type bioreactor. Conclusions: Although urease activity significantly decreased upon covalent immobilization onto modified Florisil. However, high storage stability and reusability of immobilized urease makes it potentially useful immobilized form.