D-xylose catabolizing enzymes in Neurospora crassa and their relationship to D-xylose fermentation

Summary The induction of xylose reductase (XR) and xylitol dehydrogenase (XD) activities by D-xylose under different fermentation conditions was investigated in Neurospora crassa. The induction of NADPH-linked XR preceded NADH-linked XR and the ratio of NADH to NADPH-linked XR activity displayed variation from 0.02 to 0.2 suggesting the presence of two separate enzymes. Aerobic conditions were required by N. crassa for cell growth but not for ethanol production. Maximum ethanol of 0.3 g/g of D-xylose was produced when shifted to semiaerobic condition, where high NADH-linked XR and NAD-linked XD activities were observed.