Aspergillus niger NAD(P)H-dependent D-xylose reductase xyl1 (XR, EC 1.1.1.307) is a founding member of aldo-keto reductase family 2 member D1 (AKR2D1). It catalyzes the initial reaction in the xylose utilization pathway by reducing D-xylose into xylitol in a NAD(P)H dependent manner.