The Influence Of Chitosan Molecular Weight On Immobilized Urease And Study Of Chitosan Microsphere's Form

Chitosan has many properties as carrier in enzyme immobilization. The influence of chitosan molecular weight to characters of immobilized urease is studied.Entrapment of urease is accomplished through xanthan and chitosan co-polymerized in form of hydrogel. Six kind of chitosan are used in entrapment experiment: 1-6 chitosan's molecular weight is 214577, 1 71113,154627, 136198, 118962 and 97666 in turn, they have same extent of deacetylation as 96.3%. Immobilization improved the thermal. PH and storage stability of the urease. Optimal temperature of free urease is 50 癈 ,as for immobilized urease the temperature is between 65 癈 and 70癈. Optimal PH of free urease is 7,for immobilized urease is 5 or 6. Compared all of the characters of immobilized urease the chitosan which molecular weight is 136198 has the best immobilization effect.In this paper urease is also covalently attached onto chitosan by GA. First, the concentration of GA and method of immobilization is studied. Big molecular weight chitosan (MW=1133598) is prepared into different state, such as power( I ), gel(II) and sponge(III). They are used as carriers in urease immobilization, and the characters of immobilized urease are compared. The best concentration of GA is 0.3%, and the best method of carrier preparation is to make chitosan into the shape of gel(II). So chitosan 1 (MW=171113), chitosan2 (MW=136198) and chitosan3 (MW=97666) are handled in this way, the characters of immobilized urease are compared also. Free urease has an optimal PH at 7,while it shifts to 5 for the immobilized urease and chitosan3 has the highest specific activity; Chitosan3 has the highest immobilization efficiency of 85.6% and the highest storage stability as well. Immobilization not only improved the thermal, PH and storage stability of the urease but also showed some trade that more small of earner's molecular weight more well of immobilization effect.Study of chitosan microsphere is another theme in this paper. A experiment is described which we take chitosan A(MW=97666) and chitosan B(MW=1133598) to form microsphere as immobilization carriers. We also carry out urease immobilization and its application in urea transformation. Smooth-surfaced chitosan microsphere was shaped well when chitosan concentration is 3% (A/B=5/1 ,w/w), TPPNa concentration is 1.5%. Porous chitosan microsphere was formed if put CaCO₃ (chitosan / CaCO₃=l/l,w/w) in chitosan solution just like above. The immobilization efficiency of porous chitosan moicroball is 16.5% higher than smooth-surfaced chitosan microsphere when we use GA to make urease covalently attached onto earners. Urea transformation efficiency of smoothed-surfaced chitosan microsphere for 300mg/ml urea solution is about 90% when reaction time is 12 minute. But as for porous chitosan microsphere the efficiency is above 99% under the same conditions.