Editing Glycogenesis (section)

===Epinephrine (adrenaline)===

{{see also|Epinephrine}}

Glycogen phosphorylase is activated by phosphorylation, whereas glycogen synthase is inhibited.

Glycogen  phosphorylase is converted from its less active "b" form to an active "a" form by the enzyme phosphorylase kinase. This latter enzyme is itself activated by protein kinase A and deactivated by phosphoprotein phosphatase-1.

Protein kinase A itself is activated by the [[hormone]] adrenaline. [[Epinephrine]] binds to a receptor protein that activates adenylate cyclase. The latter enzyme causes the formation of [[cyclic AMP]] from [[Adenosine triphosphate|ATP]]; two molecules of [[cyclic AMP]] bind to the regulatory subunit of protein kinase A, which activates it allowing the catalytic subunit of protein kinase A to dissociate from the assembly and to phosphorylate other proteins.

Returning to glycogen phosphorylase, the less active "b" form can itself be activated without the conformational change. 5'AMP acts as an allosteric activator, whereas ATP is an inhibitor, as already seen with [[phosphofructokinase]] control, helping to change the rate of flux in response to energy demand.

[[Epinephrine]] not only activates [[glycogen phosphorylase]] but also inhibits glycogen synthase. This amplifies the effect of activating glycogen phosphorylase. This inhibition is achieved by a similar mechanism, as protein kinase A acts to phosphorylate the enzyme, which lowers activity. This is known as co-ordinate reciprocal control. Refer to [[glycolysis]] for further information of the regulation of glycogenesis.