Catalyzes the initial reaction in the xylose utilization pathway by reducing D-xylose into xylitol. Xylose is a major component of hemicelluloses such as xylan. Most fungi utilize D-xylose via three enzymatic reactions, xylose reductase (XR), xylitol dehydrogenase (XDH), and xylulokinase, to form xylulose 5-phosphate, which enters pentose phosphate pathway. Also major aldose reductase in pentose and D-galactose catabolism. Reduces the pentose L-arabinose and the hexose D-galactose to their respective polyols. Responsible for extracellular beta-galactosidase formation and cellulase induction during growth on lactose. an alditol + NAD(+) = an aldose + H(+) + NADH an alditol + NADP(+) = an aldose + H(+) + NADPH NAD(+) + xylitol = D-xylose + H(+) + NADH NADP(+) + xylitol = D-xylose + H(+) + NADPH Carbohydrate metabolism; D-xylose degradation. Carbohydrate degradation; L-arabinose degradation via L-arabinitol; D-xylulose 5-phosphate from L-arabinose (fungal route): step 1/5. Regulated by carbon source. Most abundant during growth on D-xylose and L-arabinose. Belongs to the aldo/keto reductase family.