Second messengers adenylate cyclase control

The Adenylate Cyclase Second Messenger System that Controls Glycogenolysis. 

Although details will vary, in each case an agonist at its receptor activates adenylate cyclase and the second messenger cAMP is produced from ATP. cAMP activates protein kinase A and a cascade of reactions may follow. These may be metabolic reactions, as in the cases just described, or activation of a cAMP response-element protein, CREB. CREB is a transcription factor with affinity for specific sites on DNA. Control of protein synthesis follows. 

The adenylate cyclases (AC) are a family of enzymes, which catalyze the synthesis of cyclic AMP (cAMP), from ATP. Cyclic AMP, a ubiquitous molecule in mammalian cells, plays a key role in controlling a vast number of biological processes, functioning as a major second messenger. The ACs are present in bacteria, where c-AMP plays a key role in the regulation of transcription in fungi, parasites and mammalian cells. The mammalians ACs (at least nine enzymes) are structurally unrelated to the bacterial ones consisting of 12 transmembrane helices and two cytoplasmic catalytic domains. They differ from each other in their... 

The breakdown of fatty acids in (3-oxidation (see Topic K2) is controlled mainly by the concentration of free fatty acids in the blood, which is, in turn, controlled by the hydrolysis rate of triacylglycerols in adipose tissue by hormone-sensitive triacylglycerol lipase. This enzyme is regulated by phosphorylation and dephosphorylation (Fig. 5) in response to hormonally controlled levels of the intracellular second messenger cAMP (see Topic E5). The catabolic hormones glucagon, epinephrine and norepinephrine bind to receptor proteins on the cell surface and increase the levels of cAMP in adipose cells through activation of adenylate cyclase (see Topic E5). The cAMP allosterically activates... 

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