Guanylate cyclase (guanylyl cyclase, GC), which catalyzes the formation of cGMP from GTP, exists in both the soluble and particulate fractions of cells. Guanylyl cyclases signal via the production of the second messenger cGMP.
The GC family consists of particulate GC (pGC) and a nitric oxide-activated soluble GC (sGC). Seven pGC isoforms have yet been found (pGC-A to pGC-G). pGCs are activated by binding of peptide ligands to their extracellular domains. sGC is a receptor for endogenous and exogenous nitric oxide and is activated several-fold upon its binding, constituting a core enzyme in the nitric oxide signal transduction pathway. cGMP generated by sGC is an important second messenger that regulates activity of several enzymes triggering such important physiologic reactions as vasodilation, smooth muscle relaxation and platelet aggregation.