Preparation and Properties of Immobilized Urease in Gelatin Membrane

Urease was entraped in glutaraldehyde cross-linked gelatin membrane with activity of 6.07 U/g carrier and 66.1% retention of activity.The optimum conditions of immobilization were urease loading ratio 10 mg enzyme/g gelatin,ρ(gelatin)=100 g/L and φ(glutaraldehyde)=0 .5%.Properties of the immobilized urease were investigated and compared with the free enzyme.The optimum pH value was 7.0 and 6.5 for the free and the immobilized urease respectively.The optimum temperature was 60 ℃ for the free urease,while it shifted to 70 ℃ for the immobilized enzyme.Michaelis constant K_m was 11.7 mM and 12.4 mM for the immobilized urease and the free enzyme respectively.At 80 ℃ after 180 minutes,a complete loss of activity of the free enzyme was recorded while the immobilized urease retained 10% of its initial activity.The enzyme activity of the immobilized urease decreased by only 15% even after repeated use for 20 times,and the immobilized urease stored at 4 ℃ retained 55% of its initial activity even after 35 d.