Amino acid dehydrogenases comprise a group of coenzyme-dependent enzymes that catalyze the reversible oxidative deamination of an amino acid to its keto acid and ammonia with the concomitant reduction of either cofactor NAD+, NADP+ or FAD. The enzyme with dehydrogenase properties is distributed in a number of diverse prokaryotic and eukaryotic organisms. Amino acid dehydrogenases have been studied widely because of their potential applications in biosensors or diagnostic kits, synthesis of L- and D-amino acids for use in production pharmaceutical peptides, herbicides and insecticides (Brunhuber et al., 1994, Crit. Rev. Biochem. Mol. Biol. 29(6):415-467; Hummel et al., 1989, Eur. J. Biochem. 184:1-13; Krix et al., 1997, J. Biotech. 53:29-39; Ohshima et al., 1990, Adv. Biochem. Eng. Biotechnol. 42:181-209; U.S. Pat. No. 7,550,277). For example, the anti-hypertensives ramipril, enalapril, benazapril, and prinivil are prepared using L-homophenylalanine, and certain second generation pril analogs are synthesized from p-substituted-L homophenylalanine. Certain β-lactam antibiotics use substituted D-phenylglycine side chains, and while other antibiotics are based on aminoadipic acid and other unnatural amino acids. The unnatural amino acids L-tert-leucine, L-nor-valine, L-nor-leucine, L-2-amino-5-[1,3]dioxolan-2yl-pentanoic acid have been used as a precursor in the synthesis of a number of different developmental drugs. The enzyme leucine dehydrogenase and mutants thereof have been shown to be capable of catalyzing the reductive amination of the corresponding 2-ketoacids of alkyl and branched-chain amino acids, and L-tert-leucine has been produced commercially with such an enzyme.
Given the industrial utility of L- and D-amino acid dehydrogenases, it is desirable to develop processes and systems that can enhance the biocatalytic reactions carried out by amino acid dehydrogenases.