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Eukaryotic Cell, February 2003, p. 170-180, Vol. 2, No. 1
1535-9778/03/$08.00+0 DOI: 10.1128/EC.2.1.170-180.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Marco Sonderegger,2 Kurt Wüthrich,1 Thomas Szyperski,3* and Uwe Sauer2
Institute of Molecular Biology and Biophysics,1 Institute of Biotechnology, ETH Zürich, CH-8093 Zürich, Switzerland,2 Department of Chemistry, State University of New York, Buffalo, New York 142603
Received 13 August 2002/ Accepted 28 October 2002
The so far largely uncharacterized central carbon metabolism of the yeast Pichia stipitis was explored in batch and glucose-limited chemostat cultures using metabolic-flux ratio analysis by nuclear magnetic resonance. The concomitantly characterized network of active metabolic pathways was compared to those identified in Saccharomyces cerevisiae, which led to the following conclusions. (i) There is a remarkably low use of the non-oxidative pentose phosphate (PP) pathway for glucose catabolism in S. cerevisiae when compared to P. stipitis batch cultures. (ii) Metabolism of P. stipitis batch cultures is fully respirative, which contrasts with the predominantly respiro-fermentative metabolic state of S. cerevisiae. (iii) Glucose catabolism in chemostat cultures of both yeasts is primarily oxidative. (iv) In both yeasts there is significant in vivo malic enzyme activity during growth on glucose. (v) The amino acid biosynthesis pathways are identical in both yeasts. The present investigation thus demonstrates the power of metabolic-flux ratio analysis for comparative profiling of central carbon metabolism in lower eukaryotes. Although not used for glucose catabolism in batch culture, we demonstrate that the PP pathway in S. cerevisiae has a generally high catabolic capacity by overexpressing the Escherichia coli transhydrogenase UdhA in phosphoglucose isomerase-deficient S. cerevisiae.
Present address: Department of Molecular Biology and Genetics, Istanbul Technical University, TR-80626 Maslak, Istanbul, Turkey.
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