Immobilization of Urease onto Modified Egg Shell Membrane through Cross Linking

Abstract

Background: Immobilization is an approach in industry to improve stability and reusability of urease. The efficiency of this technique depends on the type of membrane and the method of stabilization. Methods: The PEI-modified egg shell membrane was used to immobilize urease by absorption and glutaraldehyde cross-linking methods. The membranes were characterized by FTIR and AFM, and Nessler method was applied to measure the kinetic of the immobilized enzymes. Finally, the storage stability (6 degrees C for 21 days) and reusability (until enzyme activity reached to zero) of the immobilized enzymes were investigated. Results: Based on FTIR, three new peaks were observed in both the absorption- (at 1389.7, 1230.8, and 1074.2 cm(-1)) and the cross-linking (at 1615-1690, 1392.7, 1450 cm(-1)) immobilized enzymes. The surface roughness of the native membrane was altered after PEI treatment and enzyme immobilization. The optimal pH of cross-linking immobilized enzymes was shifted to a more neutral pH, while it was alkaline in adsorption-immobilized and free enzymes. The reaction time decreased in all immobilized enzymes (100 min for free enzyme vs. 60 and 30 min after immobilizing by adsorption and cross-linking methods, respectively). The optimal temperature for all enzymes was 70 degrees C and they had a higher K-m and a lower V-max than free enzyme. The stability and reusability of urease were improved by both methods. Conclusion: Our findings propose these approaches as promising ways to enhance the urease efficiency for its applications in industries and medicines.