The present invention relates to preparation of key drug intermediate, L-2-amino butyric acid (L-2-ABA) by a method of cell free system and biotransformation using genetically engineered strains from easily available economic substrates like citramalate or citraconate and enzymes like LeuCD, LeuB and ValDH or IlvE.

The present invention relates to preparation of key drug intermediate, L-2-amino butyric acid (L-2-ABA) by a method of cell free system and biotransformation using genetically engineered strains from easily available economic substrates like citramalate or citraconate and enzymes like LeuCD, LeuB and ValDH or IlvE.

The present invention relates to a modified dehydrogenase, wherein one or more amino acid residues of the dehydrogenase are modified as compared to an unmodified dehydrogenase, and wherein the modified dehydrogenase has an increased ratio of leucine dehydrogenase or isoleucine dehydrogenase activity to valine dehydrogenase activity as compared to the unmodified dehydrogenase, and applications thereof.