page_title: Cyclic nucleotide
section_title: Synthesis and Degradation
hierarchical_section_title: Cyclic nucleotide / Biochemistry / Synthesis and Degradation
caption_attribution_description: English: Hydrolisis of 3' cNMP phosphodiester bond by phosphodiesterase
context_page_description: A cyclic nucleotide is a single-phosphate nucleotide with a cyclic bond arrangement between the sugar and phosphate groups. Like other nucleotides, cyclic nucleotides are composed of three functional groups: a sugar, a nitrogenous base, and a single phosphate group. As can be seen in the cyclic adenosine monophosphate and cyclic guanosine monophosphate images, the 'cyclic' portion consists of two bonds between the phosphate group and the 3' and 5' hydroxyl groups of the sugar, very often a ribose.
  Their biological significance includes a broad range of protein-ligand interactions. They have been identified as secondary messengers in both hormone and ion-channel signalling in eukaryotic cells, as well as allosteric effector compounds of DNA binding proteins in prokaryotic cells. cAMP and cGMP are currently the most well documented cyclic nucleotides, however there is evidence that cCMP is also involved in eukaryotic cellular messaging. The role of cyclic uridine monophosphate is even less well known.
  Discovery of cyclic nucleotides has contributed greatly to the understanding of kinase and phosphatase mechanisms, as well as protein regulation in general.
context_section_description: Cyclic nucleotides are produced from the generic reaction NTP → cNMP + PPᵢ, where N represents a nitrogenous base.  The reaction is catalyzed by specific nucleotidyl cyclases, such that production of cAMP is catalyzed by adenylyl cyclase and production of cGMP is catalyzed by guanylyl cyclase.  Adenylyl cyclase has been found in both a transmembrane and cytosolic form, representing distinct protein classes and different sources of cAMP.
  Both cAMP and cGMP are degraded by hydrolysis of the 3' phosphodiester bond, resulting in a 5'NMP.  Degradation is carried out primarily by a class of enzymes known as phosphodiesterases (PDEs).  In mammalian cells, there are 11 known PDE families with varying isoforms of each protein expressed based on the cell's regulatory needs.  Some phosphodiesterases are cNMP-specific, while others can hydrolyze non-specifically. However, the cAMP and cGMP degradation pathways are much more understood than those for either cCMP or cUMP.  The identification of specific PDEs for cCMP and cUMP has not been as thoroughly established.
caption: Generic hydrolisis reaction of 3' cNMP phosphodiester bond by phosphodiesterase
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