Anonymous
06-05-2004, 07:03 PM
Question 5: Enzyme Phosphorylation Induced by Glucagon
The same enzymes that are dephosphorylated by insulin action (namely glycogen synthase, glycogen phosphorylase, the PFK-2/FBPase-2 bifunctional enzyme and pyruvate kinase) are phosphorylated via glucagon and/or epinephrine action. Which kinase is responsible for these phosphorylation events?
A. Protein kinase C
B. Calmodulin-dependent protein kinase
C. Protein kinase A
D. Receptor tyrosine kinase
E. b-ARK
Glucagon Acts Via cAMP
http://www.biology.arizona.edu/biochemistry/problem_sets/carbomet/graphics/05t.gif
Even though glucagon is a peptide, not a catecholamine, the glucagon receptor can almost be considered to be an adrenergic receptor, in that it is linked via Gs to adenylate cyclase. The cAMP second messenger that results from this linkage activates a kinase, very imaginatively named "cAMP-dependent protein kinase" or protein kinase A. This enzyme then phosphorylates all of the enzymes that insulin may have previously dephosphorylated. Thus, the concept that insulin and glucagon have opposite actions has a definite biochemical basis!
ans:
C. Protein kinase A
This is a very clear example of how glucagon and epinephrine oppose the actions of insulin. Also, the general rule that insulin promotes dephosphorylation, while glucagon promotes phosphorylation via cAMP/protein kinase A, will hold up very well throughout the course.
The same enzymes that are dephosphorylated by insulin action (namely glycogen synthase, glycogen phosphorylase, the PFK-2/FBPase-2 bifunctional enzyme and pyruvate kinase) are phosphorylated via glucagon and/or epinephrine action. Which kinase is responsible for these phosphorylation events?
A. Protein kinase C
B. Calmodulin-dependent protein kinase
C. Protein kinase A
D. Receptor tyrosine kinase
E. b-ARK
Glucagon Acts Via cAMP
http://www.biology.arizona.edu/biochemistry/problem_sets/carbomet/graphics/05t.gif
Even though glucagon is a peptide, not a catecholamine, the glucagon receptor can almost be considered to be an adrenergic receptor, in that it is linked via Gs to adenylate cyclase. The cAMP second messenger that results from this linkage activates a kinase, very imaginatively named "cAMP-dependent protein kinase" or protein kinase A. This enzyme then phosphorylates all of the enzymes that insulin may have previously dephosphorylated. Thus, the concept that insulin and glucagon have opposite actions has a definite biochemical basis!
ans:
C. Protein kinase A
This is a very clear example of how glucagon and epinephrine oppose the actions of insulin. Also, the general rule that insulin promotes dephosphorylation, while glucagon promotes phosphorylation via cAMP/protein kinase A, will hold up very well throughout the course.