Cyclic guanosine monophosphate

Cyclic guanosine monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). cGMP acts as a hormones to the external cell surface.

Synthesis

cGMP synthesis is nitric oxide to stimulate cGMP synthesis.

Effects

cGMP is a common regulator of vasodilation and increased blood flow.

cGMP is a secondary messenger in phototransduction in the eye. In the photoreceptors of the mammalian eye, the presence of light activates sodium ion channels in photoreceptors are cGMP-gated, so degradation of cGMP causes sodium channels to close, which leads to the hyperpolarization of the photoreceptor's plasma membrane and ultimately to visual information being sent to the brain.

Degradation

Cyclic nucleotide hydrolyzing cGMP into 5'-GMP.

Sildenafil (Viagra) enhances the vasodilatory effects of cGMP within the corpus cavernosum by inhibiting PDE 5 (or PDE V). This is used as a treatment for erectile dysfunction. However, the drug can inhibit PDE6 in retina with less affinity than PDE5, so it may lead blue vision.

Protein kinase activation

cGMP is involved in the regulation of some protein-dependent kinases. For example, PKG (catalytic and one regulatory unit, with the regulatory units blocking the active sites of the catalytic units.

cGMP binds to sites on the regulatory units of PKG and activates the catalytic units, enabling them to phosphorylate their substrates. Unlike with the activation of some other protein kinases, notably PKA, the PKG is activated but the catalytic and regulatory units do not disassociate.

References

• Francis SH, Corbin JD (1999). "Cyclic nucleotide-dependent protein kinases: intracellular receptors for cAMP and cGMP action.". Crit Rev Clin Lab Sci 36 (4): 275-328. PMID 10486703.

See also

• Cyclic adenosine monophosphate (cAMP)