[WG21:p292]
Glycogen is a branched glucose polymer with 2 types of links
Glucose 6-phosphate
[Phosphoglucomutase]
---> Glucose 1-phosphate
[UDPGlc pyrophosphorylase]
===> Uridine diphosphate glucose (UDPGlc)
[Glycogen synthase]
===> Glycogen
Glycogen
[Phosphorylase a]
===> Glucose 1-phosphate
[Phosphoglucomutase]
---> Glucose 6-phosphate
Glucagon in liver
=> activates adenylyl cyclase (via Gs protein)
=> Increase in cAMP
Epinephrine in liver and muscles
=> activates adenylyl cyclase (via beta-2 receptor)
=> Increase in cAMP
=> activates cAMP-dependent protein kinase
cAMP-dependent protein kinase
(? aka protein kinase)
* Activates phosphorylase kinase, and thus phosphorylase
* Inactivates glycogen synthase
Thus, glycogenolysis
... include
All of these effects inhibit glycolysis and encourage gluconeogenesis.
In tissues other than liver, there is no glucose 6-phosphatase
Thus,
=> glucose 6-phosphate builts up
=> increased glucose catabolism
(via Embden-Meyerhof pathway and hexose monophosphate shunt)
=> increased lactate production
Glycogen synthase converts glucose 1-phosphate to glycogen
Active: glycogen synthase a (dephosphorylated)
Inactive: glycogen synthase b (phosphorylated)
Opposite to phosphorylase and phosphorylase kinase
Phosphorylase kinase activates phosphorylase
Phosphorylase converts glycogen to glucose 1-phosphate
Active: phosphorylase a (phosphorylated)
Inactive: phosphorylase b (dephosphorylated)
Similarly,
Active: phosphorylase kinase a (phosphorylated)
Inactive: phosphorylase kinase b (dephosphorylated)
Epinephrine via alpha1 receptor
=> increase intracellular [Ca2+]
=> activates phosphorylase kinase
Glucagon
* act on liver
=> increased glucose
Epinephrine
* Act on liver and muscles
* via alpha1 receptor
--> Activate adenylyl cyclase
=> increased glucose and lactate level in blood
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Created | 20050514 |