FIG 6.

Changes in metabolic fluxes in central carbon metabolism predicted by a genome-scale model of E. coli. The measurements of extracellular metabolites shown in Fig. 5 were used to compute uptake and secretion rates under each of the conditions, as outlined in Materials and Methods. These rates were used to constrain the exchange fluxes of a genome-scale model of E. coli metabolism (29), while the rate of the biomass reaction was set to the experimentally determined growth rate. We used metabolic flux analysis to define a space of solutions consistent with the measured fluxes and the stoichiometry structure of the metabolic network. This solution space was sampled in a random and unbiased manner using a Monte Carlo approach (see Materials and Methods). (a) Scatter plot of the predicted fluxes for 64 reactions in central carbon metabolism of the wild-type E. coli strain growing on glucose, in the absence and presence of acetate. Under each condition, the fluxes have been normalized by the growth rate. The scatter plot shows a very strong correlation between the predicted flux distributions in the absence and presence of acetate, with all reactions clustered around the diagonal (R² = 0.89). (b) Same as panel a, except the Δacs pta strain (R² = 0.94) was examined. (c) Same as panel a, except the Δacs pta ackA strain (R² = 0.94) was examined.