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Urease and AlaDH enzymes immobilized on active PEG derivatives were encapsulated at different ratios within sheep erythrocytes and their activity, encapsulation yields and erythrocyte recovery levels were assessed. Encapsulated derivatives were administered at given dosages and at given intervals to sheep having raised blood urea levels as a result of addition of urea to their feed, and the lowering of their blood urea levels and the change in the amount of ammonia were followed. Results were analyzed using day related NPar. Wilcoxon Signet Ranks test. It was found that 1 ml of PEG-enzyme preparation comprising PEG-urease/PEG-AlaDH at an activity ratio of 3/9 U:U/ml remained active for a period of 2 days, whereas 1 ml erythrocyte preparation, prepared under the same conditions and containing PEG-urease/PEG-AlaDH at an activity ratio of 2.15/4.5 U:U/ml, showed activity for a period of 6 days. It was shown that a single dose achieved a daily decrease of 21.7-61.6 mg/L in the blood urea level, and created no significant increase in the blood ammonia levels. No antigenic effect was observed for the PEG-enzyme preparations in the immunological test carried out.

In our system, urease/AlaDH have been encapsulated within erythrocytes by using slow dialysis methods. Urea is decomposed into ammonia and bicarbonate and the ammonia released is converted into alanine by reacting pyruvate under the catalytic action of AlaDH. It is very important for our that products are formed quickly but the ammonia is not connected definetely. For this aim, urease/AlaDH we encapsulated using different enzyme activity ratio (0.5:1.5; 0.5:2.5; 0.25:1.25 U/U urease/AlaDH). The activities of enzyme systems, encapsulation yield, McV, McH, and McHc were measured for each sample. Investigated results suggest that loaded enzyme systems can be used as potential carrier systems for the removal of high levels of urea from blood.

Urease (E.C 3.5.1.5) was covalently immobilized on activated methoxypolyethyleneglycol-5000 which is linear, uncharged, soluble in water and nonimmunogenic. mPEG is bound to the epsilon-NH2 groups of Lysin in urease. Previously different molar ratios of urease -Lys/activated-mPEG were searched for immobilization. Storage stabilities, molecular weights and the values of blocked amino groups were determined for each immobilized urease and the best conditions was found 1:3 urease-Lys/activated mPEG. Furthermore physical characterization, kinetic constants (Km, Vmax), heat and temperature stabilites were also determined.