Expression of xyrA gene encoding for D-xylose reductase of Candida tropicalis and production of xylitol in Escherichia coli

The D-Xylose reductase (XR) gene (xyrA) of Candida tropicalis IFO 0618 was expressed in Escherichia coli JM109. The enzymatic properties of each recom binant XR such as the K-m value for D-xylose and NADPH, the substrate speci ficity for other sugars and the optimal pH were essentially the same as tho se of the corresponding enzyme of C. tropicalis. The recombinant XR was mor e heat-stable than C: tropicalis XR at 60 degrees C. E. coli, expressing th e xyrA gene, successfully converted D-xylose to xylitol. When D-xglose (50 g/l) and D-glucose (5 g/l) were added to IPTG-induced cells, 13.3 g/l of xy litol was produced during 20 h of cultivation.