Cyclic GMP

In response to extracellular signals, guanylyl cyclase converts the nucleotide GTP to cyclic GMP. It is an intracellular signalling molecule. For example, in the smooth muscle of blood vessels, NO binds to the iron in the active site of guanlyl cyclase, activating the enzyme and leading to the production of cyclic GMP. In response to this the blood vessel dilates. Cyclic GMP is broken down to GMP by cyclic GMP phosphodiesterase.