Examples of blocked reactions (dashed lines) and a fully coupled enzyme subset (heavy lines). Flux v4 is blocked due to the absence of a reaction consuming metabolite H, whereas v9 and v10 are blocked because there are no reactions forming I or consuming K. Note, however, that v4 can carry flux if metabolite H is allowed to accumulate (i.e., unsteady-state). Assuming that the biomass composition is prespecified, knowledge of any flux in the enzyme subset confers the values of all other fluxes in that subset. For example, if v5 is fixed, then v6 and vbio are also fixed, as they are the only outlets for the flux towards metabolites C and F, respectively. Similarly, fluxes v7 and vE are fixed as a consequence of fixing vbio and v6.
