Detecting and investigating substrate cycles in a genome-scale human metabolic network

Authors

  • Juliane Gebauer,

    1.  Department of Bioinformatics, School of Biology and Pharmaceutics and JenAge Research Core, Friedrich Schiller University of Jena, Germany
    2.  Research Group Theoretical Systems Biology, School of Biology and Pharmaceutics, Friedrich Schiller University of Jena, Germany
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  • Stefan Schuster,

    1.  Department of Bioinformatics, School of Biology and Pharmaceutics and JenAge Research Core, Friedrich Schiller University of Jena, Germany
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  • Luís F. de Figueiredo,

    1.  Department of Bioinformatics, School of Biology and Pharmaceutics and JenAge Research Core, Friedrich Schiller University of Jena, Germany
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    • These authors contributed equally to this work

    • Present address
      Cheminformatics and Metabolism, European Bioinformatics Institute (EBI), Wellcome Trust Genome Campus, Cambridge, UK

  • Christoph Kaleta

    1.  Department of Bioinformatics, School of Biology and Pharmaceutics and JenAge Research Core, Friedrich Schiller University of Jena, Germany
    2.  Research Group Theoretical Systems Biology, School of Biology and Pharmaceutics, Friedrich Schiller University of Jena, Germany
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    • These authors contributed equally to this work


C. Kaleta, Research Group Theoretical Systems Biology, School of Biology and Pharmaceutics, Leutragraben 1, Friedrich Schiller University of Jena, D-07743 Jena, Germany
Fax: +49 3641 949595
Tel: +49 3641 949590
E-mail: christoph.kaleta@uni-jena.de

Abstract

Substrate cycles, also known as futile cycles, are cyclic metabolic routes that dissipate energy by hydrolysing cofactors such as ATP. They were first described to occur in the muscles of bumblebees and brown adipose tissue in the 1970s. A popular example is the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate and back. In the present study, we analyze a large number of substrate cycles in human metabolism that consume ATP and discuss their statistics. For this purpose, we use two recently published methods (i.e. EFMEvolver and the K-shortest EFM method) to calculate samples of 100 000 and 15 000 substrate cycles, respectively. We find an unexpectedly high number of substrate cycles in human metabolism, with up to 100 reactions per cycle, utilizing reactions from up to six different compartments. An analysis of tissue-specific models of liver and brain metabolism shows that there is selective pressure that acts against the uncontrolled dissipation of energy by avoiding the coexpression of enzymes belonging to the same substrate cycle. This selective force is particularly strong against futile cycles that have a high flux as a result of thermodynamic principles.

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