CONVERSION OF AMMONIA OR UREA INTO ESSENTIAL AMINO-ACIDS, L-LEUCINE, L-VALINE, AND L-ISOLEUCINE USING ARTIFICIAL CELLS CONTAINING AN IMMOBILIZED MULTIENZYME SYSTEM AND DEXTRAN-NAD+ - L-LACTIC DEHYDROGENASE FOR COENZYME RECYCLING

A multienzyme system consisting of leucine dehydrogenase (EC 1.4.1.9), L-lactic dehydrogenase (EC 1.1.1.27), urease (EC 3.5.1.5), and dextran-NAD+ was microencapsulated within artificial cells. This system could convert ammonia and urea into essential amino acids, L-leucine, L-valine, and L-isoleucine. L-lactate acted as a cosubstrate for the regeneration of dextran-NADH. Greater concentrations of L-lactate favored the higher conversion ratios. The effects of ammonium salts and urea on reaction rate were also studied. The relative reaction rates in ammonium salts solutions were 44.6-78.8% of those in urea solutions. More than 90% of the original activity was retained when artificial cells were kept at 4°C for 6 wk. © 1990 Humana Press Inc.