Anonymous
06-05-2004, 07:06 PM
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
We are dealing here with the major action of epinephrine to mobilize glycogen from liver (shown), and also muscle (which lacks PFK-2 and glucose-6-phosphatase). The context is acute stress, so the liver's role is to release fuel into the blood, while muscle would then use the fuel, from either the liver or from its own glycogen stores, for the "fight or flight response".
The coordinate regulation of glucose metabolism is via phosphorylation, the opposite of insulin's action via dephosphorylation. As you will recall, the Gs/cAMP/protein kinase A pathway is involved in many important phosphorylation events, including the ones here. Recall also that epinephrine, unlike the peptide hormone glucagon,is a catecholamine and thus must bind to an adrenergic receptor.
Which adrenergic receptor subtype(s) act via Gs?
http://www.biology.arizona.edu/biochemistry/problem_sets/carbomet/graphics/06t.gif
ans:
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...
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
We are dealing here with the major action of epinephrine to mobilize glycogen from liver (shown), and also muscle (which lacks PFK-2 and glucose-6-phosphatase). The context is acute stress, so the liver's role is to release fuel into the blood, while muscle would then use the fuel, from either the liver or from its own glycogen stores, for the "fight or flight response".
The coordinate regulation of glucose metabolism is via phosphorylation, the opposite of insulin's action via dephosphorylation. As you will recall, the Gs/cAMP/protein kinase A pathway is involved in many important phosphorylation events, including the ones here. Recall also that epinephrine, unlike the peptide hormone glucagon,is a catecholamine and thus must bind to an adrenergic receptor.
Which adrenergic receptor subtype(s) act via Gs?
http://www.biology.arizona.edu/biochemistry/problem_sets/carbomet/graphics/06t.gif
ans:
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...