Network representation of E. coli core metabolism. This reconstruction refers to the work of Orth et al. and maintains the same notation. Metabolites are in ellipses (yellow color: external nutrients; blue color: cytoplasmatic compounds) and reactions in boxes (dark gray for irreversible and light gray for reversible processes). Nodes highlighted with red border belong to Krebs cycle. For a better readability, common species like water, Oxygen, H+, Ammonium, CO2, phosphate, NAD (in all forms), Coenzyme-A, AMP, ADP and ATP, as well as all transport and exchange processes, have been excluded from the representation.