Revisiting the13C-label distribution of the non-oxidative branch of the pentose phosphate pathway based upon kinetic and genetic evidence

Roelco J. Kleijn, Wouter A. Van Winden, Walter M. Van Gulik, Joseph J. Heijnen

Research output: Contribution to journalArticleScientificpeer-review

Abstract

The currently applied reaction structure in stoichiometric flux balance models for the nonoxidative branch of the pentose phosphate pathway is not in accordance with the established ping-pong kinetic mechanism of the enzymes transketolase (EC 2.2.1.1) and transaldolase (EC 2.2.1.2). Based upon the ping-pong mechanism, the traditional reactions of the nonoxidative branch of the pentose phosphate pathway are replaced by metabolite specific, reversible, glycolaldehyde moiety (C2) and dihydroxyacetone moiety (C 3) fragments producing and consuming half-reactions. It is shown that a stoichiometric model based upon these half-reactions is fundamentally different from the currently applied stoichiometric models with respect to the number of independent C2 and C3 fragment pools in the pentose phosphate pathway and can lead to different label distributions for 13C-tracer experiments. To investigate the actual impact of the new reaction structure on the estimated flux patterns within a cell, mass isotopomer measurements from a previously published 13C-based metabolic flux analysis of Saccharomyces cerevisiae were used. Different flux patterns were found. From a genetic point of view, it is well known that several microorganisms, including Escherichia coli and S. cerevisiae, contain multiple genes encoding isoenzymes of transketolase and transaldolase. However, the extent to which these gene products are also actively expressed remains unknown. It is shown that the newly proposed stoichiometric model allows study of the effect of isoenzymes on the 13C-label distribution in the non-oxidative branch of the pentose phosphate pathway by extending the half-reaction based stoichiometric model with two distinct transketolase enzymes instead of one. Results show that the inclusion of isoenzymes affects the ensuing flux estimates.

Original languageEnglish
Pages (from-to)4970-4982
Number of pages13
JournalThe FEBS Journal
Volume272
Issue number19
DOIs
Publication statusPublished - Oct 2005

Keywords

  • C labeling
  • Metabolic flux analysis
  • Pentose phosphate pathway
  • Transaldolase
  • Transketolase

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