Immobilization of Urease onto Modified Egg Shell Membrane through Cross Linking

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.

The PEI-modified egg shell membrane was used to immobilize urease by absorption and glutaraldehyde cross-linking methods. The membranes were characterized by Fourier-transform infrared spectroscopy (FTIR) and AFM, and Nessler method was applied to measure the kinetic of the immobilized enzymes. Finally, the storage stability (6 °C for 21 days) and reusability (until enzyme activity reached to zero) of the immobilized enzymes were investigated.  

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 °C and they had a higher Km and a lower Vmax than free enzyme. The stability and reusability of urease were improved by both methods.

Our findings propose these approaches as promising ways to enhance the urease efficiency for its applications in industries and medicines.