Comparison of measured metabolic fluxes and in-vitro enzyme activities. Measured flux rates (blue, mmol/h/g dry biomass) and in vitro enzyme activities (red, U/mg protein) on two separate Y-axes of selected reactions in the central metabolism of E. coli are shown as a function of growth/dilution rates (X-axis). All labels are as in Figure 3. Additional file 2 shows the actual data on measured enzyme activities. The error bars for the experimental flux and enzyme activity plots are a result of three independent measurements.