CO-EXPRESSION OF XYLOSE REDUCTASE GENE FROM Candida shehatae AND ENDOGENOUS XYLITOL DEHYDROGENASE GENE IN Saccharomyces cerevisiae AND THE EFFECT OF METABOLIZING XYLOSE TO ETHANOL

摘要

The inability of Saccharomyces cerevisiae to utilize xylose is attributed to its inability to convert xylose to xylulose. Low xylose reductase (XR) and xylitol dehydrogenase (XDH) activities in S. cerevisiae are regarded as the reason of blocking thepathway from xylose to xylulose. We had found that Candida shehatae could also be another source for XRgene except Pichia stipitis in the previous study. In this study, we tried to investigate if the expressed XR from C. shehatae could work with the over-expressed endogenous XDH together to achieve the same goal of converting xylose to ethanol in S. cerevisiae. The XR gene (XYL1) from C. shehatae and endogenous XDH gene (XYL2) were both cloned and over-expressed in host S. cerevisiae cell. The specificenzyme activities of XR and XDH were measured and the result of fermentation revealed that the new combination of two enzymes from different sources other than P. stipitis could also coordinate and work with each other and confer xylose utilization ability to S. cerevisiae.