earticle

영어

Transaminase (TA) catalyzes transfer of an amino group between amino acids and α-keto acids. The TA can be divided into two classes depending on the position of the amino group in an amino donor relative to the carboxyl group, i.e. α-TA and ω-TA. The TA requires pyridoxal 5'-phosphate (PLP) as a cofactor. The TA has gained increasing attention owing to high turnover rate, precise enantioselectivity and no cofactor requirement. To develop novel biocatalytic processes for production of unnatural amino acids, we cloned three bacterial ω-TAs selected by amino acid sequence homology using the well-studied w-TA from Vibrio fluvialis JS17. The three ω-TAs from Paracoccus denitrificans, Ochrobactrum anthropi and Pseudomonas stutzeri were cloned into pET28 expression vector. Despite of high sequence homology, the three ω-TAs showed very similar enzymatic properties including substrate specificity, optimal pH and
inhibitions by substrates and products. Benzylamine and (S)-a-ethylbenzylamine ((S)-a-EBA) are the best amino donors among the ones tested. In the case of amino acceptor specificity, the ω-TAs show high activities towards 2-oxobutyricacid, pyruvate, butanal and benzaldehyde. Strong substrate inhibitions by pyruvate and butanal were observed whereas substrate inhibition by amino donors including (S)-a-EBA and benzylamine was moderate. In the case of product inhibition, benzaldehyde and propiophenone exerted high enzyme inhibition. The optimum pH and temperature for the enzymes were 9 and 37 oC, respectively. We carried out asymmetric
synthesis of L-2-aminobutyric acid using 2-oxobutyricacid (10 mM) and benzylamine (20 mM) as substrates and the conversion yield reached 79, 69 and 76 % using the ω-TAs from P. denitrificans, O. anthropi and P. stutzeri, respectively, after 5 h reaction.