Illustrative example network. Illustrative example network containing the metabolites A to E, P, Q and S, the reactions R1 to R12, and the genes GR1, GR2, GR5a, GR5b, GR7a, GR7b, GR8, GR10, and GR11. All reactions are irreversible, except for R7. Transition from E to C is defined as the forward direction of R7. Small numbers in the edges of reactions indicate stoichiometric coefficients, if they are different from one. All metabolites inside the shaded area are considered internal and are subject to the steady state condition. Gene-enzyme-reaction mapping is indicated by dashed lines. Reaction R5 is catalyzed by an enzyme complex encoded by gene GR5a and GR5b. Reaction R7 is catalyzed by two enzymes encoded by GR7a or GR7b. The reaction R10 is catalyzed by GR10. However, activity of R10 is inhibited if GR1 is expressed. For the reaction R3, R4, R6, R9 and R12 no gene-enzyme-reaction mapping is available.