Effect of D-glucose on induction of xylose reductase and xylitol dehydrogenase in Candida tropicalis in the presence of NaCl
✍ Scribed by Tomohiko Ikeuchi; Rie Kiritani; Masayuki Azuma; Hiroshi Ooshima
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 129 KB
- Volume
- 40
- Category
- Article
- ISSN
- 0233-111X
No coin nor oath required. For personal study only.
✦ Synopsis
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. D-Xylose arises from the hydrolysis of lignocellulosic biomass and can be used as the raw material for xylitol or ethanol production. Xylitol is a five-carbon sugar alcohol that has a degree of sweetness equal to that of sucrose, as well as having anticariogenic properties. Xylitol is currently produced by the chemical reduction of D-xylose from hemicellulose hydrolysates. However, this process is expensive due to the fact that D-xylose must be purified before reduction.
Xylitol can be produced from D-xylose by yeast, such as the genus Candida . The first two steps in xylose metabolism are catalyzed by NAD(P)H-dependent xylose reductase (XR) (E.C. 1.1.1.21) and NAD(P)