PRODUCTION OF ESSENTIAL L-BRANCHED-CHAIN AMINO-ACIDS IN BIOREACTORS CONTAINING ARTIFICIAL CELLS IMMOBILIZED MULTIENZYME SYSTEMS AND DEXTRAN-NAD+

We prepared artificial cells each containing leucine dehydrogenase (EC 1.4.1.9), urease (EC 3.5.1.5), soluble dextran–NAD+, and one of the following coenzyme regenerating dehydrogenases: glucose dehydrogenase (EC 1.1.1.47); yeast alcohol dehydrogenase (EC 1.1.1.1); malate dehydrogenase (EC 1.1.1.37); or lactate dehydrogenase (EC 1.1.1.27). Artificial cells were packed in small columns. L‐Leucine, L‐valine, and L‐isoleucine were continuously produced with simultaneous dextran–NADH regeneration. The maximum production ratios depended on the coenzyme regenerating systems used: 83–93% for D‐glucose and glucose dehydrogenase system; 90% for ethanol and yeast alcohol dehydrogenase system; 45–55% for L‐malate and malate dehydrogenase system; and 64–78% for L‐lactate and lactate dehydrogenase system. Kinetic experiments were also carried out. The apparent Km values are as follows: 0.33 mM for α‐ketoisocaproate (KIC); 0.51 mM for α‐ketoisovalerate (KIV); 0.58 mM for DL‐α‐keto‐β‐methyl‐n‐valerate (KMV); 3.52 mM for urea; 27.82 mM for D‐glucose; 3.89 mM for ethanol; 3.02 mM for L‐malate; and 16.67 mM for L‐lactate. Kinetic analysis showed that KIC, KIV, and KMV were all competitive inhibitors in the reactions catalyzed by leucine dehydrogenase. Their inhibitor constants were the corresponding Km values. Copyright © 1990 John Wiley & Sons, Inc.