Stoichiometric network constraints on xylose metabolism by recombinant Saccharomyces cerevisiae

Yong Su Jin, Thomas W. Jeffries

Research output: Contribution to journalArticlepeer-review


Metabolic pathway engineering is constrained by the thermodynamic and stoichiometric feasibility of enzymatic activities of introduced genes. Engineering of xylose metabolism in Saccharomyces cerevisiae has focused on introducing genes for the initial xylose assimilation steps from Pichia stipitis, a xylose-fermenting yeast, into S. cerevisiae, a yeast traditionally used in ethanol production from hexose. However, recombinant S. cerevisiae created in several laboratories have used xylose oxidatively rather than in the fermentative manner that this yeast metabolizes glucose. To understand the differences between glucose and engineered xylose metabolic networks, we performed a flux balance analysis (FBA) and calculated extreme pathways using a stoichiometric model that describes the biochemistry of yeast cell growth. FBA predicted that the ethanol yield from xylose exhibits a maximum under oxygen-limited conditions, and a fermentation experiment confirmed this finding. Fermentation results were largely consistent with in silico phenotypes based on calculated extreme pathways, which displayed several phases of metabolic phenotype with respect to oxygen availability from anaerobic to aerobic conditions. However, in contrast to the model prediction, xylitol production continued even after the optimum aeration level for ethanol production was attained. These results suggest that oxygen (or some other electron accepting system) is required to resolve the redox imbalance caused by cofactor difference between xylose reductase and xylitol dehydrogenase, and that other factors limit glycolytic flux when xylose is the sole carbon source.

Original languageEnglish (US)
Pages (from-to)229-238
Number of pages10
JournalMetabolic Engineering
Issue number3
StatePublished - Jul 2004
Externally publishedYes


  • Extreme pathways
  • Flux balance analysis
  • Metabolic phenotype

ASJC Scopus subject areas

  • Biophysics
  • Bioengineering
  • Endocrinology, Diabetes and Metabolism


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