Conservation within the global metabolic network. An integrated view of metabolism in which individual enzymes (1,329 nodes) are connected through common metabolites (5,906 edges) (see Materials and methods). Colors of nodes represent which metabolic superclass (as defined by KEGG) each enzyme belongs to (see inset key). Node size indicates the number of genomes (of 167 complete genomes) in which the enzyme could be detected. A number of pathways with connected enzymes are indicated with red circles for illustrative purposes. While some nodes such as those involved in diterpenoid biosynthesis - pathway 11 - form a separate network, the vast bulk of metabolic pathways form connections with many others (for example, Nitrogen metabolism - pathway 21).