1. 3 Intracellular metabolic fluxes in a tpi1Δnde1,2Δgut2ΔSaccharomyces cerevisiae strain determined by independently fitting the mass isotopomer fractions of the intracellular metabolites measured by LC-MS (top values, bold), by independently fitting the mass isotopomer fractions of the proteinogenic amino acids measured by GC-MS (top-middle values, italic), by independently fitting the relative intensities of the proteinogenic amino acids measured by NMR (bottom-middle values, bold italic) and by fitting the combined ¹³C-labelling dataset (NMR, LC-MS and GC-MS) (bottom values, normal). Fluxes are normalized for the glucose uptake rate. Values outside parentheses denote the net fluxes, while values in parentheses represent the exchange fluxes. Solid arrowheads denote the direction of the net flux. Abbreviations: FBP, fructose-1,6-bisphospate; P5P, pentose-5-phopshate; S7P, sedoheptulose-7-phosphate; E4P, erythrose-4-phosphate; E-C₂, glycolaldehyde moiety covalently bound to the thiamine pyrophosphate/transketolase complex; E-C₃, dihydroxyacetone moiety covalently bound to the enzyme transaldolase; ser, serine; gly, glycine; thr, threonine; other abbreviations as in Fig. 1.
Metabolic flux analysis of a glycerol-overproducing Saccharomyces cerevisiae strain based on GC-MS, LC-MS and NMR-derived 13C-labelling data
FEMS Yeast Res. 2007;7(2): doi: /j x
FEMS Yeast Res | © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved

2. 1 Intracellular metabolic fluxes in a tpi1Δnde1,2Δgut2ΔSaccharomyces cerevisiae strain quantified via metabolite balancing. The strain was grown in an aerobic, glucose-limited chemostat culture at D=0.05 h⁻¹. Fluxes were determined by combining the measured conversion rates with a standard stoichiometric model (model 1, bold) and an extended stoichiometric model containing a putative NADH-shuttle and the methylglyoxal bypass (model 8, italic). Apart from the carbon flow through the primary metabolism, the NADH production or consumption is specified for each reaction. Fluxes are normalized for the glucose uptake rate. Abbreviations: glc, glucose; G6P, glucose-6-phosphate; F6P, fructose-6-phosphate; PPP, pentose phosphate pathway; DHAP, dihydroxyacetone phosphate; GAP, glyceraldehyde-3-phosphate; goh, glycerol; PEP, phosphoenol pyruvate; pyr, pyruvate; aald, acetaldehyde; etoh, ethanol; AcCoA, acetyl-CoA; OAA, oxaloacetate; citr, citrate; akg, α-ketogluterate.
Metabolic flux analysis of a glycerol-overproducing Saccharomyces cerevisiae strain based on GC-MS, LC-MS and NMR-derived 13C-labelling data
FEMS Yeast Res. 2007;7(2): doi: /j x
FEMS Yeast Res | © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved

3. 2 Online measurement of the ¹³CO₂/¹²CO₂ ratio in the offgas of a aerobic glucose-limited chemostat culture of a tpi1Δnde1,2Δgut2ΔSaccharomyces cerevisiae strain. After 4.25 residence times the naturally labelled feed was replaced by a chemically identical feed, but enriched in ¹³C. Samples to measure the isotopic enrichment of the intracellular components were harvested four residence times later.
Metabolic flux analysis of a glycerol-overproducing Saccharomyces cerevisiae strain based on GC-MS, LC-MS and NMR-derived 13C-labelling data
FEMS Yeast Res. 2007;7(2): doi: /j x
FEMS Yeast Res | © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved

4. 4 Contribution of the LC-MS, GC-MS and NMR datasets to the minimized sum of squared residuals (SS_res) as calculated via ¹³C-labelling-based MFA. Minimized SS_res values were first derived for each individual dataset (indv.), after which combinations (comb.) of the ¹³C datasets were used for flux estimation.
Metabolic flux analysis of a glycerol-overproducing Saccharomyces cerevisiae strain based on GC-MS, LC-MS and NMR-derived 13C-labelling data
FEMS Yeast Res. 2007;7(2): doi: /j x
FEMS Yeast Res | © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved

5. 5 Observed fold increase in SS_res when independently refitting the LC-MS, GC-MS and NMR ¹³C-labelling data for fixed values of (a) the PPP split-ratio, (b) the pyruvate carboxylase catalysed flux, (c) the reversibility of the oxaloacetate transporter and (d) the pyruvate decarboxylase catalysed flux. Metabolic flux estimates for the LC-MS dataset were limited to glycolysis and the PPP. As a result, the sensitivities of nodes b, c and d were not analysed for the LC-MS dataset.
Metabolic flux analysis of a glycerol-overproducing Saccharomyces cerevisiae strain based on GC-MS, LC-MS and NMR-derived 13C-labelling data
FEMS Yeast Res. 2007;7(2): doi: /j x
FEMS Yeast Res | © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved

6. 6 Observed fold increase in total SS_res (a) and SS_res of the individual datasets (b) when refitting the combined LC-MS, GC-MS and NMR ¹³C-labelling data for fixed values of the biosynthetic efflux from the G6P pool. Estimated values for the PPP split-ratio and the methylglyoxal bypass flux for the different biosynthetic G6P effluxes are given in (a).
Metabolic flux analysis of a glycerol-overproducing Saccharomyces cerevisiae strain based on GC-MS, LC-MS and NMR-derived 13C-labelling data
FEMS Yeast Res. 2007;7(2): doi: /j x
FEMS Yeast Res | © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved