Nonproteinogenic α-Amino Acid Preparation Using Equilibrium Shifted Transamination

Abstract

Microbial α-transaminases such as tyrosine aminotransferase (TAT) and branched chain aminotransferase (BCAT) of Escherichia coli, are useful as industrial biocatalysts to prepare nonproteinogenic l-amino acids from α-keto acids and an amino donor. However, they typically yield only 50% product when l-glutamic acid, the preferred amino donor, is used due to accumulated 2-ketoglutaric acid. Accordingly, methods have been sought to increase the reaction yield by the recycle or removal of the keto acid by-product. In this report, we have investigated the biocatalytic coupling of δ-transamination with α-transamination to recycle 2-ketoglutaric acid, and thereby increase the yield of aminotransferase reaction products. Ornithine δ-aminotransferase (OAT) catalyses the reversible transfer of the δ-amino group of l-ornithine to 2-ketoglutaric acid forming l-glutamic acid semialdehyde and l-glutamic acid. The cyclisation of l-glutamic acid semialdehyde to form Δ1-pyrroline-5-carboxylate under physiological conditio...