Epinephrine, released in response to exercise, will lead to phosphorylation events that will ultimately exert which of the following effects on hepatic glycogen metabolism?

Question

Quizplus · Accepted Answer

Epinephrine activates phosphorylase kinase, which in turn activates glycogen phosphorylase, promoting glycogen breakdown in the liver. Epinephrine can bind and activate both α-adrenergic and β-adrenergic receptors. When epinephrine binds α1-adrenergic receptors, there is an activation of the membrane-associated enzyme PLC-β. PLC-β hydrolyzes membrane PIP₂ into DAG and IP₃. The IP₃ then binds to receptors present in membranes of the endoplasmic reticulum (ER), resulting in release of stored calcium ion. The released calcium binds to the calmodulin subunit of glycogen synthase-phophorylase kinase, resulting in activation of this regulatory enzyme. The net effect is enhanced activity of phosphorylase and inhibited activity of glycogen synthase. When epinephrine binds β-adrenergic receptors, there is activation of adenylate cyclase resulting in increased cAMP with consequent activation of PKA. PKA phosphorylates and activates glycogen synthase-phoshorylase kinase with the results being the same as for α₁-adrenergic receptor activation.

Epinephrine, Released in Response to Exercise, Will Lead to Phosphorylation