The Study Of Combination-assembly-immobilization Of Urease

Urease is present in abundance of jackbean’ seeds which catalyzes decomposition of urea to produce ammonia and carbon dioxide. Urease immobilization has been a prerequisite for industries based on enzyme hydrolyzed products, it has been successfully implemented at lab scales for enzyme stabilization from various environment factors including pH, temperature, buffers, etc. Several methods of enzyme immobilization have been known,each of them has their own weakness and strength.Adsorption is simple,cheap and effective but frequently reversible, covalent and cross-linking are effective and durable, but expensive and easily worsening the enzyme activity,and in membrane reactor-confinement,entrapment and micro--encapsulations diffusional problems are inherent. Principlally, as a standard the optimal immobilization conditions for a chosen enzyme and its application are done empirically by a process of trial.Meanwhile, the matrixs chosen which are non-toxic, cheap, renewable and biodegradable.In this work, chitosan and some hydrophilic polymers were mainly chosen as matrixs.and blended with them in different ratio to form different shape including gelatin.microsphere and micro membrane. The methods of immobilization contained adsorption-crosslink, entrapment-crosslink and CLEA, meanwhile SEM and Automatic Contact Angle measure device were used to observe the structure and pore distribution on the surface and cross-section, the change of hydrophilicity on the chitosan matrix surface. Immobilization methods above were compared, the best one was chitsoan/PEG=1micro membrane. Uniform and thoroughfare pores had formed on the membrane which enlarged the specific surface area and enhanced the relative activity which had reached to102.75%. The measurement of contact angle on chitosan/PEG membrane showed that the hydrophilicity of membrane surface had changed after urease adsorption and relative activity was higer than other chitosan matrix sharply, the effect of immobilization was103.72U/(cm2·min) which revealed that urease was adsorbed on chitosan membrane successfully.