File:AutoPhospho.jpg

A bi-stable molecular switch. a. A schematic diagram of an autophosphorylation loop. Here is is assumed that binding phosphorylation activates the kinase, this active kinase in turn phosphorylates more of the kinase. This kinase can be dephosphorylated by a kinase. This positive feedback might produce bistability, however; such a simple autophosphorylation loop might not actually be bistable. b. One candidate molecule for an autophosphorylation loop is CaMKII. CaMKII molecules form into holoenzymes composed of two rings with ~6 CaMKII subunits in each ring. Neighboring CaMKII molecules can phosphorylate each other. Initial activation of CaMKII requires Ca-CaM, but active states have much longer lifetimes when phophorylated.