Lecture 22 - Glycobiology 3 - Regulation of Glycogen Metabolism Flashcards
(15 cards)
How is glycogen regulated
Regulated both through the rate of synthesis and degradation of glycogen
Regulated by phosphorylation and dephosphorylation of the key regulatory enzymes
What enzyme synthesises glycogen
Glycogen Synthase
What enzyme degrades glycogen
Glycogen Phosphorylase
What is the reaction cascade for glycogen metabolism
1 signal molecule
10 second messengers activated
100 molecules activated
1000 glucose released
What effect does insulin have upon glycogen synthase
increases activity of enzyme
increases conversion of GS form its phosphorylated b form (inactive) to its dephosphorylated a form (active)
What is GSK3
Glycogen Synthase Kinase 3
What does GSK3 do
Inactivates GS by adding phosphate groups to Ser side chains
Inactivates GS by adding phosphate groups to Ser side chains
What can GSK3 not do which is unusual for a kinase
Cannot add P to unphosphorylated GS
(this is unusual for kinases)
GS ‘primed’ by Casein kinase II (CKII) -then GSK3 adds 4 further phosphates
What is the removal of phosphates from Glycogen synthase catalysed by
Phosphoprotein phosphatase 1 (PP1)
PP1 acts quicker if what is bound to GS?
G-6-P
so G-6-P is considered an activator of GS
What is the signal for degradation
Glucagon signals liver to release glucose into the blood
Adrenaline (epinephrine) signals muscles to release glucose for energy production
What is Glycogen Phosphorylase activated by in muscles
Ca2+ – released in muscles to induce contraction stimulates phosphorylase kinase
AMP – builds up in muscle if not enough ATP being produced
What effects does PP1 have on the regulation of glycogen
PP1 increases activity of GS by dephosphorylating it
PP1 decreases activity of GP by dephosphorylating it
What is PP1 inhibited by
Phosphorylated by PKA (protein Kinase A
What is PP1 bound to what along with its 3 main substrates, which are?
Glycogen particle
GS, PK and GP
(held together attached to glycogen by glycogen-targeting protein)
