Optimal Fluxes, Reaction Replaceability, and Response to Enzymopathies in the Human Red Blood Cell

Figure 1

Bipartite graph representation of a reaction network, with circles (resp. squares) denoting reactions (resp. metabolites). Here, reaction 𝑅 uses metabolites 𝑎 and 𝑎^ as substrates to produce metabolite 𝑏. If 𝑅 is removed, the conversion of 𝑎 to 𝑏 is still permitted by the alternative pathway 𝑎→𝑐→𝑑→𝑒→𝑏. When 𝑅 is fictitiously reversed, this chain forms a directed loop of length 5 reactions, formed by 𝑅 and by a path passing through ℓ=4 other reactions.