en Enzymology and Protein Chemistry Enzymology and Protein Chemistry مقاله کامل Full Length/Original Article <strong>Background:</strong> 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.<br> <strong>Methods:</strong> 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 &deg;C for 21 days) and reusability (until enzyme activity reached to zero) of the immobilized enzymes were investigated. &nbsp;<br> <strong>Results:</strong> 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<em>.</em> 60 and 30 min after immobilizing by adsorption and cross-linking methods, respectively). The optimal temperature for all enzymes was 70 &deg;C and they had a higher K_mand a lower V_max than free enzyme. The stability and reusability of urease were improved by both methods.<br> <strong>Conclusion:</strong> Our findings propose these approaches as promising ways to enhance the urease efficiency for its applications in industries and medicines. Egg shell, Immobilization, Polyethylenimine, Urease 132 141 http://ibj.pasteur.ac.ir/browse.php?a_code=A-10-3403-1&slc_lang=en&sid=1 Fatemeh Morovvat faezeh.amr@gmail.com 0000-0001-5529-9466 No Isfahan University Of Medical Sciences, Isfahan, Iran Seyed Ziaeddin Samsam Shariat* samsam@pharm.mui.ac.ir 0000-0002-9324-5626 No Isfahan University Of Medical Sciences, Isfahan, Iran Maryam Davoudi ar_ty2002@yahoo.com 0000-0002-1048-1237 No Pilot Nano- Biotechnology Department- Pasteur Institute of Iran Dariush Norouzian dnsa@pasteur.ac.ir 0000-0002-3553-3048 Yes Pilot Nano- Biotechnology Department- Pasteur Institute of Iran