Comparison of the ω-transaminases from different microorganisms and application to production of chiral amines

Microorganisms that are capable of (S)-enantioselective transamination of chiral amines were isolated from soil samples by selective enrichment using (S)-alpha -methylbenzylamine ((S)-alpha -MBA) as a sole nitrogen source. Among them, Klebsiella pneumoniae JS2F, Bacillus thuringiensis JS64, and Vibrio fluvialis JS17 showed good to-transaminase (omega -TA) activities and the properties of the omega -TAs were investigated. The induction level of the enzyme was strongly dependent on the nitrogen source for the strains, except for V fluvialis JS17. All the omega -TAs showed high enantioselectivity (E>50) toward (S)-alpha -MBA and broad amino donor specificities for arylic and aliphatic chiral amines. Besides pyruvate, aldehydes such as propianaldehyde and butyraldehyde showed good amino acceptor reactivities. All the omega -TAs showed substrate inhibition by (S)-alpha -MBA above 200 mm. Moreover, substrate inhibition by pyruvate above 10 mm was observed for omega -TA from V. fluvialis JS17. In the ease of product inhibition, acetophenone showed much greater inhibitions than L-alanine for all omega -TAs. Comparison of the enzyme properties indicates that omega -wtransaminase from V. fluvialis JS17 is. the best one for both kinetic resolution and asymmetric synthesis to produce enantiomerically pure chiral amines. Kinetic resolution of sec-butylamine (20 mm) was done under reduced pressure (150 Torr) to selectively remove an inhibitory product (2-butanone) using the enzyme from V. fluvialis JS17. Enantiomeric excess of (R)-sec-butylamine reached 94.7% after 12 h of reaction.