Figure 2.

Diagram of the components and reactions in the proposed dynamical model of pectin catabolism. The two metabolites, cAMP and KDG, indirectly activate the expression of pel genes by binding their associated regulators: cAMP allows CRP to bind and activate the promoters, whereas KDG relieves KdgR repression, respectively. Pel enzymes are instantaneously exported and degrade PGA (pectin) into UGA (unsaturated galacturonides), which is imported and converted into KDG, triggering a positive feedback loop. KdgR is synthesized at a constant rate. CRP, cAMP receptor protein; KDG, 2-keto-3-deoxygluconate; Pel, endo-pectate lyase; PGA, polygalacturonate.