Optimal (A) and non-optimal (B) reaction activity in the reconstructed metabolic network of E. coli in glucose minimal medium (Materials and Methods).

The pie charts show the fractions of active and inactive reactions in the metabolic subsystems defined in the iJR904 database [75]. The color code is as follows: active reactions (red), inactive reactions due to mass balance (black) and environmental constraints (blue), inactive reactions due to the irreversibility (green) and cascading (yellow) mechanisms, and conditionally inactive reactions (orange), which are inactive reactions that can be active for other growth-maximizing states under the same medium condition. The optimal state shown in panel A was obtained by flux balance analysis (FBA, see Materials and Methods). The network is constructed by drawing an arrow from one subsystem to another when there are at least 4 metabolites that can be produced by reactions in the first subsystem and consumed by reactions in the second. Larger pies represent subsystems with more reactions.