Effect ofD-glucose on induction of xylose reductase and xylitol dehydrogenase inCandida tropicalis in the presence of NaCl

Abstract

Xylitol production is suppressed by D-glucose. We previously reported that the suppression was abrogated in the presence of NaCl. This was explained in part by high levels of xylose reductase (XR) activity. In this study, we investigated the effects of D-glucose on XR and xylitol dehydrogenase (XDH) induction in Candida tropicalis in the presence of NaCl. We examined the time courses of these activities under the following conditions: 50 mg/ml D-xylose, 20-80 mg/ml D-glucose and 40 mg/ml NaCl. The level of XR increased in the presence of 40 mg/ml NaCl, whereas that of XDH was not affected by NaCl. The effects of NaCl upon XR and XDH induction suggest that the synthesis of both enzymes is not under a coordinate control. The expression of XR is suppressed by D-glucose. In the absence of NaCl, suppression continued even after D-glucose was completely consumed, while in the presence of 40 mg/ml NaCl, suppression stopped after the consumption of D-glucose.