FIGURE 2.

Metabolic model of a three-enzyme pathway (A) A three-enzyme metabolic pathway model is reported with the result of the flux balance analysis. The rank of the stoichiometric matrix S is 4, so that the degree of freedom of the algebraic system obtained by applying the stationary condition for homeostasis is 2. Therefore, only two fluxes, J _P and J _Q must be determined to know the stationary rates of all the processes at homeostasis. (B) On the top left, the time courses of the metabolite concentrations and of the rates of the transport processes are reported against time, showing a cell with a normal radius r ₀ as it reaches homeostasis; on the top right, a metabolic map with the flux distribution at homeostasis is sketched; on the bottom left, stationary concentrations of different metabolites are shown, and on the bottom right the values of the fluxes are reported as diverse histograms for cells with an increasing ratio of r/r ₀ .