Carbohydrate Metabolism Regulation Problem Set
Question 2: Enzymes Dephosphorylated by Insulin Action
Tutorial to help answer the question
Of the enzymes of carbohydrate metabolism listed below, which are (de)phosphorylated
in liver in response to insulin signaling?
- Glycogen synthase
- Glycogen phosphorylase
- Phosphofructokinase-1 (PFK-1)
- Phosphofructokinase-2 (PFK-2)
- Pyruvate kinase
Tutorial
Four of the six enzymes named in the above figure are dephosphorylated
in response to insulin. These enzymes are denoted by a red -OH, signifying
that the phosphate group has been removed from the serine or threonine residue
in the enzyme, leaving a free hydroxyl. Recall that enzyme dephosphorylation
is often the way in which enzymes are ultimately regulated by insulin (don't
worry about the exact mechanism for now - there are too many steps between
insulin binding and activation of the protein phosphatase).
In three of the four cases, the enzyme is activated by dephosphorylation. The
exception is found in the glycogen synthase/phosphorylase pair, which obviously
cannot both be activated at the same time. However, you don't necessarily have
to memorize which one is inhibited by insulin - this can be reasoned through
by considering which way the reaction should go in times of high blood glucose.
You guessed it, toward glucose storage (i.e., glycogen synthesis).
Problem 2 | Answer | Problem
3
Vocabulary
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March 16, 2001
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