Figure 1. Levels of metabolic organization.

(A) Catalytic domains accelerate one or few biochemical reactions; (B) enzymatic complexes may form homomultimers or heteromultimers, by organizing enzymatic domains to efficiently perform more complicated catalytic reactions. For example, by homomultimerization of enzymatic domains, enzyme complexes achieve efficient catalysis of higher concentrations of metabolites. Heteromultimerization may co-localize sequential metabolic enzymes of parts of metabolic pathways. (C) A complete metabolic pathway may be organized on scaffold molecules and its participating enzymes transiently interact to form an assembly of its individual components, therefore achieving regulation of the metabolic pathway as function of cellular needs. (D) Enzymatic complexes and metabolons may be confined in membrane-less or membrane-bound organelles, therefore, further increasing catalytic efficiency or localizing specialized metabolic processes (see text).