Cyclic adenosine monophosphate (cAMP, cyclic AMP or 3'-5'-cyclic adenosine monophosphate) is a molecule that is important in many biological processes; it is derived from adenosine triphosphate (ATP).
cAMP is a second messenger, used for intracellular signal transduction, such as transferring the effects of hormones like glucagon and adrenaline, which cannot get through the cell membrane. Its main purpose is the activation of protein kinases; it is also used to regulate the passage of Ca2+ through ion channels.
cAMP synthesis and decomposition
cAMP is synthesized from ATP by adenylate cyclase. Adenylate cyclase is located at the cell membranes. It is activated by the hormones glucagon and adrenaline and by G protein. Liver adenylate cyclase responds more strongly to glucagon, and muscle adenylic cyclase responds more strongly to adrenaline.
cAMP decomposition into AMP is catalyzed by the enzyme phosphodiesterase. This enzyme is inhibited by caffeine, the stimulatory effect of this drug being the result of the raised cAMP levels that it causes.
Protein kinase activation
cAMP is involved some protein-dependent kinases. For example, PKA (protein kinase A), as a holoenzyme is inactive and exists as a tetramer , consisting of 2 catalytic and 2 regulatory units (C2R2), with the regulatory units blocking the catalytic centers of the catalytic units.
cAMP binds to specific locations on the regulatory units of the protein kinase, and causes dissociation between the regulatory and catalytic subunits, thus activating the catalytic units and enabling them to phosphorylate substrate proteins.
Glycogen decomposition regulation
cAMP controls many biological processes, including glycogen decomposition into glucose, and lipolysis.
Role of cAMP in bacteria
In bacteria, cAMP is produced when the level of glucose in the cell is low; it activates the production of enzymes that can supply glucose.