Prospects of Application of D-amino Acid Transaminase from Aminobacterium colombiense for (R)-selective Amination of α‑Keto Acids

D-amino acid transaminase from Aminobacterium colombiense was applied for (R)-selective amination of 2-oxobutyrate, 2-oxovalerate and 2-oxo-4-phenylbutyrate to produce non-natural D-amino acids—D-homoalanine, D-norvaline and D-homophenylalanine. To increase the product yield of D-amino acids, a one-pot three-enzyme system was developed. The system included transaminase from A. colombiense, (R)-2-hydroxyglutarate dehydrogenase and glucose dehydrogenase and effectively shifted the equilibrium of transamination reaction toward the products. The system functioned at both neutral and slightly alkaline pH. We found that at high substrate concentrations (500 mM) transaminase from A. colombiense was inhibited by the products accumulated in the system. The optimization of operational conditions of the three‑enzyme system led to the following yields of the target products: 435 mM D-homoalanine, 320 mM D-norvaline and 47.5 mM D-homophenylalanine; the enantiomeric excess of the produced D-amino acids exceeded 99.5%.