Carbohydrate Metabolism Regulation Problem Set

Question 2: Enzyme Dephosphorylaton by Insulin Action

Of the enzymes of carbohydrate metabolism listed below, which are (de)phosphorylated in liver in response to insulin signaling?

1. Glycogen synthase

2. Glycogen phosphorylase

3. Phosphofructokinase-1 (PFK-1)

4. Phosphofructokinase-2 (PFK-2)

5. Pyruvate kinase

   Four of these enzymes are directly modified via dephosphorylation (1, 2, 4, and 5). Three of the dephosphorylation events activate the affected enzyme, but one (glycogen phosphorylase) is inhibited by this modification. Again, this makes sense in view of insulin's role to store, not mobilize glucose. The remaining enzyme is affected indirectly by insulin, but how?

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