Anonymous
06-05-2004, 06:56 PM
Of the enzymes of carbohydrate metabolism listed below, which are dephosphorylated in liver in response to insulin signaling?
[check all that apply]
Glycogen synthase
Glycogen phosphorylase
phosphofructokinase-1 (PFK-1)
phosphofructokinase-2 (PFK-2)
pyruvate kinase
Dephosphorylation as a Frequent Endpoint of Insulin Action
http://www.biology.arizona.edu/biochemistry/problem_sets/carbomet/graphics/02t.gif
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).
ans:
Glycogen synthase
Glycogen phosphorylase
phosphofructokinase-2 (PFK-2)
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?
[check all that apply]
Glycogen synthase
Glycogen phosphorylase
phosphofructokinase-1 (PFK-1)
phosphofructokinase-2 (PFK-2)
pyruvate kinase
Dephosphorylation as a Frequent Endpoint of Insulin Action
http://www.biology.arizona.edu/biochemistry/problem_sets/carbomet/graphics/02t.gif
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).
ans:
Glycogen synthase
Glycogen phosphorylase
phosphofructokinase-2 (PFK-2)
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?