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. 2017 Oct 12;5:e3860. doi: 10.7717/peerj.3860

Figure 4. Network redundancies: example of sustainability and producibility-PEMs that are not optimal-efficiency PEMs.

Figure 4

In the A. ferrooxidans network, the production of glycogen and lps_AFE can be handled by two alternative pairs of reactions, either through α-g6p (α-D-Glucose-6-phosphate) or through β-g1p (β-D-1-phosphate). β-g6p (β-D-Glucose-6-phosphate) is not an optimal-efficient PEM because removing any of the two reactions which consuming it has no impact on the optimal production of the biomass components. On the contrary, removing both reactions, as allowed by Definition 3 for sustainability and producibility PEMs, implies that the biomass components cannot be produced. Therefore, β-g6p is a sustainability and a producibility PEM.