New Approaches Using Immobilized Enzymes for the Removal of Urea and Ammonia

Abstract

The microcapsule artificial kidney is the smallest artificial kidney available at present (1,2). Its completion requires only a urea removal system. Other compact artificial kidney systems would also require a compact urea removal system (3,4). Extensive study is therefore being carried out to find effective methods for the removal of urea. One of the earlier approaches involving the use of enzyme was demonstrated here as early as 1964 when artificial cells containing urease was shown to act in vivo to convert urea in the body fluid to ammonia (5). It can also be used in extracorporeal systems to lower the systemic blood urea in dog to 50 percent in 90 minutes and ammonia formed was removed by hemoperfusion through microencapsulation ammonia absorbent (6). This principle of combined use of urease and ammonia adsorbent was later adapted for use in the Reddy dialysate regeneration system where the constrains of a large priming volume is not a factor in dialysate regeneration (7). The use of microencapsulated urease for oral ingestion has also been studied (8–11). Recent studies in this laboratory involve two other new approaches for the enzymatic removal of urea, (a) Using artificial cells containing multienzyme system with cofactor recycling, urea or ammonia have been sequentially converted into amino acids (12–14). (b) Urea was enzymatically converted into ammonium, which was converted by alkalinization into ammonia that is extracted as ammonia gas (15).