Regulation of Carbohydrate Metabolism Problem Set

Question 6: Epinephrine action to mobilize glycogen

To which receptor does epinephrine bind in order to stimulate phosphorylation of glycogen synthase, glycogen phosphorylase, PFK-2/FBPase-2 bifunctional enzyme, and pyruvate kinase?

A.	alpha-1
B.	alpha-2
C.	glucagon
D.	beta One way to arrive at the correct answer is to recall that the actions of epinephrine resemble that of glucagon in opposing insulin. However, since epinephrine is a catecholamine, its receptor must be distinct from the glucagon receptor, which binds a polypeptide ligand. Otherwise, the similarity with glucagon holds, in that both agents exert their effects on the liver (or muscle) cell by raising cAMP to activate protein kinase A. For the purposes of the Biochemistry course (but not necessarily Physiology!), do not worry about the distinction between beta-1 and beta-2. But there is more to the epinephrine story...