cAMP is a second messenger molecule, used for intracellular signal transduction. It is made from ATP by adenylate cyclase. Its main purpose is the activation of protein kinases; it is also used to regulate the passage of Ca2+ through ion channels, a mechanism used in smelling by mammals.
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cAMP's decomposition into [adenosine monophosphate]? is catalyzed by the phosphodiesterase? enzyme. This enzyme is inhibited by caffeine, the stimulatory efffect of this drug being the result of the raised cAMP levels that it causes.
cAMP controls many biological processes, including glycogen? decomposition into glucose, and lipolysis?.
Adenylate cyclase is located at the cell's membranes. It is activated by the hormones glucagon? and adrenaline. These hormones can't go through the cell membrane, so all their activity is mediated by cAMP. Liver's adenylate cyclase reacts more strongly to glucagon?, and muscle's [adenylic cyclase]? reacts more strongly to adrenaline.
In Bacteria, cAMP is a hormone of hunger?. It is created if the level of glucose in the cell is low and it activates the production of enzymes that might possibly supply glucose.