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. 2021 Feb 9;12:586293. doi: 10.3389/fgene.2021.586293

FIGURE 2.

FIGURE 2

Schematic description of the ReFill algorithm. New reaction annotations are added only if all the metabolites are connected to the existing network. A connected metabolite is denoted in a green circle. An orphan (unconnected metabolite) is denoted in a red circle. (A) A simple case in which all the metabolites comply with the selection rule. (B) In case one or more metabolites are not connected to the existing network, other new reactions may be added to complete the missing connections. For example, consider reaction a to be composed of two substrates and two products, one of which, x (a metabolite that did not exist in the initial network), is not connected to the existing network and is currently an orphan. After the expansion step, the algorithm identified one reaction, b, in which x is used as a substrate. All other metabolites in b exist in the network thus creating a path from reaction a through reaction b to the network.