the cofactor imbalance between the NAD(P)H-dependent wild type XR and NAD+-dependent XDH can create an intracellular redox imbalance, leading to an accumulation of NADH and a shortage of NAD+ necessary for the XDH reaction. The likely increase in intracellular xylitol concentration favors xylitol excretion, which reduces the ethanol yield by Saccharomyces cerevisiae
engineered Sacchyromyces cerevisiae expressing NADPH-linked xylose reductase (XR) and NAD+-linked xylitol dehydrogenase (XDH) produces substantial amounts of the reduced byproducts under anaerobic conditions due to the cofactor difference of XR and XDH. While the additional expression of a water-forming NADH oxidase (NoxE) from Lactococcus lactis in engineered Saccharomyces cerevisiae with the XR/XDH pathway leads to reduced glycerol and xylitol production and increased ethanol yields from xylose, volumetric ethanol productivities by the engineered yeast decrease because of growth defects from the overexpression of noxE. High cell density inoculum for xylose fermentation by strain SR8 expressing noxE, resulting in strain SR8N, shows a higher ethanol yield and lower byproduct yields, and also exhibits a high ethanol productivity during xylose fermentation. Growth defects from noxE overexpression can be overcome in the case of fermenting lignocellulose-derived sugars such as glucose and xylosen
engineered Sacchyromyces cerevisiae expressing NADPH-linked xylose reductase (XR) and NAD+-linked xylitol dehydrogenase (XDH) produces substantial amounts of the reduced byproducts under anaerobic conditions due to the cofactor difference of XR and XDH. While the additional expression of a water-forming NADH oxidase (NoxE) from Lactococcus lactis in engineered Saccharomyces cerevisiae with the XR/XDH pathway leads to reduced glycerol and xylitol production and increased ethanol yields from xylose, volumetric ethanol productivities by the engineered yeast decrease because of growth defects from the overexpression of noxE. High cell density inoculum for xylose fermentation by strain SR8 expressing noxE, resulting in strain SR8N, shows a higher ethanol yield and lower byproduct yields, and also exhibits a high ethanol productivity during xylose fermentation. Growth defects from noxE overexpression can be overcome in the case of fermenting lignocellulose-derived sugars such as glucose and xylosen
gene XYL2, recombinant expression in Saccharomyces cerevisiae strain SCB7 resulting in strains SCF202 and SCF201, coexpression of XYL2 with XYL1, encoding a xylose reductase, and the endogenous XKS1, encoding a xylulokinase, all under the control of the TDH3 promoter in the chromosomal DNA, the recombinant strain efficiently grows in minimal medium containing xylose as the sole carbon source. An additional mutation of MTH1, encoding the endogenous negative regulator of the glucose-sensing signal transduction pathway, MTH1e32, and GRR1, encoding endogenous Grr1, an Fbox protein component of an SCF ubiquitineligase complex grr1e33, enable efficient growth in medium containing high xylose concentrations, subcloning in Escherichia coli strain DH10B
production of L-xylulose from xylitol using a resting cell reaction leads to 35% L-xylulose within 24 h, starting from 5% xylitol as initial concentration
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1.1.1.B19 xylitol dehydrogenase (NAD+)
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