Carbohydrate Metabolism Regulation Problem Set

Carbohydrate Metabolism Regulation Problem Set

Question 5: Enzyme Phosphorylation Induced by Glucagon

Tutorial to help answer the question.

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 kinase

C. Protein kinase A

D. Receptor tyrosine kinase

E. b-ARK

Tutorial

Glucagon Acts Via cAMP

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 G_s 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!

The Biology Project
The University of Arizona
March 16, 2000
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