[The preparation and application of cross-linked urease aggregates]

Urease was immobilized in a simple and effective way by physical aggregation using a precipitant-ammonium sulfate, followed by chemical cross-linking using a bifunctional reagent-glutaraldehyde to form insoluble Cross-linked urease aggregates (CLUAs). The optimum pH, optimum temperature and Km of CLUAs were 8.0, 70 degrees C and 0.021 mol/L respectively. Compared with that of free urease, the thermal stability, storage stability and resistance of cross-linked urease aggregates to the exogenous proteolysis were enhanced. The efficacy of CLUAs for the treatment of rats with chronic renal failure was also studies. The rats with chronic renal failure caused by adenine were divided into 3 groups randomly:the control group (fed with 10 mL water /kg per day), Coated Aldehyde Oxystarch (CAO) group (fed with 20 g CAO /kg and 10 mL water /kg per day) and CLUAs + CAO group (fed with 20 g CAO /kg and 10 mL CLUAs /kg per day) in which CAO was used to absorb the ammonia produced from urea. The contents of BUN and Scr in serum before and after 2 weeks treatment were determined. In three groups, the level of Scr decreased slightly (P = 0.922, 0.972 and 0.225 > 0.05 respectively) after treatment. The level of BUN was not changed (P = 0.211 > 0.05) in the control group, but decreased greatly BUN in both CAO group and CLUAs + CAO group (P = 0.004 < 0.05 and P < 0.001 respectively). Furthermore, the decrease of the BUN level after treatment in the CLUAs + CAO group was more remarkable than that in the CAO group (P = 0.016 < 0.05), which showed that the CLUAs + CAD system was more efficient than the CAO system for the removal of urea in serum.