EC Number   |
Application |
Reference |
|---|
  1.1.1.430 | synthesis |
D-xylose is the second most abundant renewable sugar in nature, and its fermentation to ethanol has great economical potential. Unfortunately, Saccharomyces cerevisiae, which has been optimized for ethanol production, cannot utilize xylose efficiently, while D-xylulose, an isomerization product of D-xylose, can be assimilated. A major strategy for constructing xylose-fermenting Saccharomyces cerevisiae is to introduce genes involved in xylose metabolism from other organisms. Xylose reductase and xylitol dehydrogenase (EC 1.1.1.9) from the xylose-fermenting yeast Pichia stipitis are cloned into Saccharomyces cerevisiae to allow xylose fermentation to ethanol. In this case, xylose is converted into xylulose by the sequential actions of two oxidoreductases. First, Pichia stipitis xylose reductase catalyses the reduction of xylose into xylitol with NAD(P)H as co-substrate. Xylitol is then oxidized by PsXDH (Pichia stipitis xylitol dehydrogenase) which uses NAD+ exclusively as co-substrate to yield xylulose. The different coenzyme specificity of the two enzymes xylose reductase and xylitol dehydrogenase, however, creates an intracellular redox imbalance, which results in low ethanol yields and considerable xylitol by-product formation. A mutant is constructed that shows an altered active site that is more unfavorable for NADPH than NADH in terms of both Km and kcat. There are potentials for application of the mutant (K270S/N272P/S271G/R276F) in constructing a more balanced xylose reductase/xylitol dehydrogenase pathway in recombinant xylose-fermenting Saccharomyces cerevisiae strains |
765348 |
| 1.1.1.430 | synthesis |
dual specific xylose reductase (dsXR) has an about 4fold higher specificity for NADH than NADPH. This fact could make this enzyme an interesting candidate to be used in metabolic engineering of the yeast xylose metabolism, likely in Saccharomyces cerevisiae. Increased levels of dsXR activity could contribute to an improvement of ethanol production from D-xylose by reducing the cofactor imbalance of the initial catabolic pathway |
764945 |
| 1.1.1.430 | synthesis |
expression of wild-type Xyl1 or an NADH-specific mutant in Saccharomyces cerevisiae. The Xyl1 mutant decreases the biocatalysts performance, suggesting use of the NADPH-preferring wild-type enzyme when (semi-)aerobic conditions are applied. In a bioreactor process, the best-performing strain converts 40 g/l xylose with an initial productivity of 1.16 g/l/h and a xylitol yield of 100% |
740171 |
| 1.1.1.430 | synthesis |
fermentation of mixed glucose-xylose substrates in Saccharomyces cerevisiae strains BP10001 and BP000, expressing Candida tenuis xylose reductase in mutated NADH-preferring form and NADPH-preferring wild-type form, respectively. Glucose and xylose, each at 10 g/l, are converted sequentially. The distribution of fermentation products from glucose is identical for both strains whereas when using xylose, BP10001 shows enhanced ethanol yield and decreased yields of xylitol and glycerol as compared to BP000. Increase in xylose concentration from 10 to 50 g/l results in acceleration of substrate uptake by BP10001 and reduction of the xylitol yield. In mixed substrate batches, xylose is taken up at low glucose concentrations and up to 5fold enhanced xylose uptake rate is found towards glucose depletion |
712951 |
| 1.1.1.430 | synthesis |
in fermentation for citric acid production and xylitol accumulation by using D-xylose as the sole carbon source, a sttrain carrying mutant K274R shows a 2.8fold reduction in xylitol accumulation and 4.5fold increase in citric acid production compared to the wild-type strain |
-, 738796 |
