Question

Acetyl CoA carboxylase activity is regulated by hormone-controlled phosphorylation and dephosphorylation.

a)  Describe the effects of epinephrine on acetyl CoA carboxylase activity and fatty acid metabolism in the liver.

b)  Is this consistent with epinephrine’s effect on liver glycogen metabolism?                  

Answer 1

a) Acetyl CoA Corboxylase (ACC) catalyses the primary reaction in fatty acid biosynthesis.

It converts acetyl CoA to malonyl CoA which is a subtrate for Fatty acid synthase enzyme.

ACC is active in dephosphorylated form and inacvtive in phosphorylated form.

cAMP dependent protein kinase inactivates ACC by phosphorylating it. Phosphatase enzyme activates ACC.

When there is low glucose level Fatty acid synthesis should be inhibited. cAMP dependent protein kinase should be activated and it is done with the help of epinephrine when it binds to G-protein coupled receptor.

Binding of Epinephrine to G-protein coupled receptor, activates adenylate cyclase and there by increases cAMP (ATP to cAMP conversion ).

Increased cAMP activates cAMP dependent protein kinase and there by inacivation of ACC.

b) Epinephrine at the same time induces glycogenolysis by activating the enzyme Glycogen phosphorylase (GP)

GP is active in phosphorylated form and the same cAMP dependent protein kinase phosphorylates GP and ativates glycogen breakdown.

So in total Epinephrine in hypogylcemic condition inhibit fatty acid synthesis and accelerates glycogen breakdown in liver.