Industrial process for ethanol production from
lignocelluloses requires that the yeast is capable of
fermenting all of the sugars present with high
ethanol yields and productivities. Although
Saccharomyces cerevisiae is naturally unable to
ferment pentoses, its capability for xylose
utilization has successfully been improved by
intensive research over the last decades. A key
aspect of metabolic engineering in yeast has been
the heterologous expression of genes for xylose
reductase (XR) and xylitol dehydrogenase (XDH)
derived from Pichia stipitis, combined with
overexpression of S. cerevisiae xylulokinase (XK);
in combination, these enzymes are responsible for