Fig. 3.

Structures of phosphodiesterases 1–5. Phosphodiesterase (PDE) 1 contains two calmodulin (CaM) binding domains, two phosphorylation sites and an inhibitory (I) region. PDE2 and PDE5 possess two cGMP-stimulated PDE, Anabaena AC and Fhla transcription factor (GAF) domains. Binding of cyclic guanosine-3′,5′-monophosphate (cGMP) to GAF-B and GAF-A stimulates the hydrolytic activity of PDE2 and PDE5, respectively. PDE3 can be phosphorylated at multiple regions, and PDE4 contains one phosphorylation site within its first upstream conserved regions (UCRs). Abbreviations: C, carboxyl-terminus; N, amino terminus; P, phosphate