Cyclic adenosine monophosphate (cAMP, or 3'-5'-cyclic
adenosine monophosphate) is derived from
adenosine triphosphate (ATP).
cAMP is a second messenger molecule, 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 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 efffect of this drug being the result of the raised cAMP levels that it causes.
In the absence of cAMP, a protein kinase is inactive and exists as a tetramer, consisting of 2
catalytic and 2 regulatory units (C
2R
2), 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, causing them to dissociate from the tetramer, thus activating the catalytic units so they can perform their function.
cAMP controls many biological processes, including
glycogen decomposition into
glucose and
lipolysis[?].
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.
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