Reductive amination by recombinant Escherichia coli: Whole cell biotransformation of 2-keto-3-methylvalerate to l-isoleucine

• For reductive amination of 2-keto-3-methylvalerate to l-isoleucine a transaminase and a l-alanine dehydrogenase were coupled in an E. coli whole cell biotransformation system.
• Complete conversion was realized by regeneration of the cofactor NADH by glucose catabolism.
• Deletions of nuoG and aceA were demonstrated to improve reductive amination.

A whole cell biotransformation system for reductive amination has been studied in recombinant Escherichia coli cells. Reductive amination of 2-keto-3-methylvalerate to l-isoleucine by a two-enzyme-cascade was achieved by overproduction of endogenous l-alanine dependent transaminase AvtA and heterologous l-alanine dehydrogenase from Bacillus subtilis in recombinant E. coli. Up to 100 mM l-isoleucine were produced from 100 mM 2-keto-3-methylvalerate and 100 mM ammonium sulfate. Regeneration of NADH as cofactor in the whole cell system was driven by glucose catabolism. The effects of defined gene deletions in the central carbon metabolism on biotransformation were tested. Strains lacking the NuoG subunit of NADH:ubiquinone oxidoreductase (complex I) or aceA encoding the glyoxylate cycle enzyme isocitrate lyase exhibited increased biotransformation rates.