Cyclic AMP (cAMP) is a cyclic nucleotide of adenosine that acts at the cellular level to regulate various metabolic processes and mediate the effects of many hormones.  


cAMP is synthesised from ATP by adenylate cyclase which is located at the cell membranes. Adenylate cyclase is activated by the hormones glucagon and adrenaline through the activation of adenylate cyclase stimulatory G (Gs)-coupled receptors and inhibited by agonists of adenylate cyclase inhibitory G (Gi)-protein coupled receptors. Liver adenylate cyclase responds more strongly to glucagon, and muscle adenylate cyclase responds more strongly to adrenaline.

cAMP decomposition into AMP is catalyzed by the enzyme phosphodiesterase.

Cyclic AMP as a Second Messenger

The neurotransmitter binds the receptor.  The receptor activates the G-protein (so-called, because it binds guanine nucleotides).  The G-protein, in turn, activates the enzyme adenylate cyclase.  Adenylate cyclase is responsible for the conversion of ATP (adenosine-tri-phosphate) to cyclic AMP.  Cyclic AMP then activates protein kinase enzymes which results in phosphorylation of proteins responsible for gene activation.