Abstract
By using DL-acetonitrile as enzyme inducer, 90 bacteria were isolated from a field soil. Among the isolated strains, the strain WJ-003 showed the highest activity for production of D-lactic acid from DL-lactonitrile, and was partially identified as Pseudomonas sp. The production condition of D-lactic acid from DL-lactonitrile using resting cells as an enzyme source was optimized as follows: the reaction mixture contained 10 mM of DL-lactonitrile, 20 g of wet cells in 11 of 20 mM potassium phosphate buffer (pH 7.0) and the reaction was carried out at $30^{\circ}C$. After 18 h of reaction, 0.843 g/l of D-lactic acid was produced which corresponded to a conversion ratio of 93.7% and an optical purity of 99.8%. Additionally, when 10 mM of DL-lactonitrile was added once more to the reaction mixture at 14 h, 1.64 g/1 of D-lactic acid was produced after 28 h. In this experiment, the conversion ratio was 91.1% and optical purity 99.8%.
Nitrile 비대칭 가수분해효소를 지닌 미생물을 이용하여 DL-lactonitrile로부터 D-lactic acid를 생산하기 위하여, DL-acetonitrile을 효소유도제로 이용할 수 있는 균주를 분리하였다. 분리한 균주들 중 WJ-003균주가 D-lactic acid의 생산능력이 가장 우수하였고, Pseudomonas sp.로 부분동정하였다. DL-lactonitrile로부터 D-lactic acid를 생산하기 위한 최적 반응조건을 검토하였으며 결과들을 요약하면 다음과 같다. 반응혼합액은 10mM의 DL-lactonitrile과 20g(wet weight)의 균체를 포함한 11의 20mM 인산완충액(pH7.0)이었으며, 이때 반응온도는 $30^{\circ}C$이었다. 또한, 18시간 반응이 진행되는 동안 0.843 g/l D-lactic acid가 생산되었고, 이때의 전환율은 93.7%,광학순도는 99.8%이었다 한편, 10mM의 DL-lactonitrile을 14시간 후에 다시 첨가했을 때 28시간에 1.64g/l의 D-lactic acid가 생산되었으며 이때의 전환율은 91.1%, 광학순도는 99.8%이었다.
