Figure 2

Graded and all-or-none interactions. A) The reaction cycle of ligand binding and phosphorylation consists of four species that are connected by four reactions. This is a general property of graded interactions. B) The processes are coupled via an all-or-none interaction. Therefore the species DOp and all corresponding rates do not exist. C) All-or-none interaction between binding site phosphorylation and effector binding. The species DOOE does not exist. D) The reaction cycle degenerates to a reaction chain which is a hallmark of all-or-none interactions. E) In this case, nomenclature can be simplified as the two sites on the receptor are essentially one.