Clone, Expression And Characterization Of A D-Xylose Reductase From Candida Tropicalis

Xylose is the second most abundant carbohydrate in nature. The efficient utilization of xylose is essential for successful turning raw materials into more value-added product by microorganisms or enzymes as active catalysts. Many microorganisms can utilize xylose as a carbon source. But only a few can ferment it. Furthermore, byproduct formation and intolerance to high product concentration is also disadvantages in large-scale fermentation. So metabolic engineering of xylose fermentation is an attractive approach, for example, yeast engineered for xylose metabolism. Because yeast is more fit for large-scale fermentation. The key to anaerobic assimilation of xylose by native yeasts was the presence of xylose reductase (EC 1.1.1.21), which could accept either NADH or NADPH as a cofactor and reducing xylose to xylitol. In general, XR is specific for NADPH, but in some cases, it can utilize both NADPH and NADH even prefers NADH than NADPH. Though the different coenzyme specificity has an effect on the metabolic flux in the xylose-fermentation recombinant strains, make the metabolism lean to product xylitol or ethanol. In order to obtain a better xylose-fermentation recombinant strain by metabolic engineering, the most important thing is obtain a high catalytic efficiency D-Xylose Reductase, then according to its cofactor preference to construct xylose-fermentation recombinant strains. In our previous study, through compared the ability of xylitol production of four different yeast strains, a high xylitol production strain C.tropicalis AY92045 was screened. When it ferments pure xylose the production efficiency is 47.30%, and after optimizing the ferment...