Schematic diagram of the construction of metabolic reaction networks. (A) A general representation of the metabolic pathway. Reactions are represented as enzymes (E1, E2, and E3) and corresponding genes (G1, G2, and G3). For example, E1:G1 means that the gene G1 encodes enzyme E1. M1, M2, and M3 correspond to metabolic compounds. C1, c2, and c3 indicate currency metabolites such as ATP and NADH. (B) The metabolic reaction network obtained from (A). (C) The metabolic reaction network is finally represented as an undirected network because of the shortest path analysis.