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glycogen synthase catalyzes glycogen synthesis. determine whether each of the following are associated with an increase or decrease in glycogen synthase activity.
a. Increased glycogen synthase activity:
b. Decreased glycogen synthase activity:
1) activation of phosphoprotein phosphatase PP1
2) Phosphorylation (inactivation) of phosphoprotein phosphatase 1 (PP1) by PKA
3) Subunit dissociation of cAMP-dependent protein kinase (PKA)
4) Phosphorylation of glycogen synthase
5) Insulin
6) Phosphorylation of glycogen synthase kinase (GSK, or GSK3)

Respuesta :

Some point in increasing or decreasing glycogen synthase activity.

Increased glycogen synthase activity:

  • Phosphorylation of glycogen synthase kinase (GSK, or GSK3).
  • activation of phosphoprotein phosphatase PP1.
  • Insulin

Decreased glycogen synthase activity:

  • Phosphorylation of glycogen synthase.
  • Phosphorylation (inactivation) of phosphoprotein phosphatase 1 (PP1) by PKA.
  • Subunit dissociation of cAMP-dependent protein kinase (PKA).

Insulin and glucagon are counter-regulatory hormones and thus have opposing effects on the level of glycogen synthase phosphorylation. When glucagon binds to receptors on hepatocytes there is a resultant increase in cAMP and a concomitant increase in PKA activity.

PKA results in phosphorylate glycogen synthase at least four different sites. In addition, PKA activity results in increased phosphorylase kinase activity on the glycogen synthase phosphorylate at one of the same sites as PKA. Insulin in PKA increases the activity of cAMP phosphodiesterase which hydrolyzes AMP thereby reducing the level of active PKA.

Insulin also exerts a negative effect on GSK-3 activity such as a decrease in the level of glycogen synthase phosphorylation by kinases.

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