Identification of a xylitol dehydrogenase gene from Kluyveromyces marxianus NBRC1777.

Xylitol dehydrogenase (XDH) (EC 1.1.1.9) is one of the key enzymes in the xylose fermentation pathway in yeast and fungi. A xylitol dehydrogenase gene (XYL2) encoding a XDH was cloned from Kluyveromyces marxianus NBRC 1777, and the in vivo function was validated by disruption and complementation analysis. The highest activity of KmXDH could be observed at pH 9.5 during 55°C. The values of k(cat)/K(m) indicate that KmXDH prefers NAD(+) to NADP(+) (k(cat)/K(m NAD)(+) 3681/min mM and k(cat)/K(m NADP)(+) 1361/min mM). The different coenzyme preference between KmXR and KmXDH caused an accumulation of NADH in the xylose utilization pathway. The redox imbalance may be one of the reasons to cause the poor xylose fermentation under oxygen-limited conditions in K. marxianus NBRC1777.