Simultaneous synthesis of enantiomerically pure (S)-amino acids and (R)-amines using coupled transaminase reactions

For the simultaneous synthesis of enatiomerically pure (S)-amino acids and (R)-amines from corresponding alpha-keto acids and racemic amines, an alpha/omega-transaminase coupled reaction system was designed using favorable reaction equilibrium shift led by omega-transaminase reaction. Cloned tyrB, aspC and avtA, and omegataA were co-expressed in E. coli BL21(DE3) using pET23b(+) and pET24ma, respectively. The coupled reaction produced the (S)-amino acids with 73-90% (> 99% ee(S)) of conversion yield and resolved the racemic amines with 83-99% ee(R) for 5 to 10 hours. In designing the coupled reactions in the cell, alanine and pyruvate were efficiently used in the cell as an amine donor for the alanine transaminase and an amino acceptor for the omega-transaminase, respectively, resulting in an alanine-pyruvate shuttling system. The common problem of the low equilibrium constant of the alpha-transaminase can be efficiently overcome by the coupling with the omega-transaminase. However, overcoming the product inhibition of omega-transaminase by the ketone by-product and increasing the decarboxylation rate of the oxaloacetate produced during the transaminase reaction become barriers to further improving the overall reaction rate and the yield of the coupled reactions.