Flux knock-out curves. Flux knock-out impact on the volume of the space of solutions in E. coli central metabolism. On the x-axis we display the percentage of reduction of any given flux, and on the y-axis the relative volume difference with respect to the unperturbed system. We use upper-case keys for internal fluxes, and lower-case to exchange fluxes. We indicate keys only for the 20 fluxes having larger impact on the volume (dots) and we display the rest fluxes with thin scattered lines.