Regulat on of glycogen metabol sm
The two key enzymes n glycogen metabol sm are:
1. Glycogen synthase for glycogenesis
2. Glycogen phosphorylase for Glycogenolysis.
These two enzymes are regulated n two ways: Alloster c sites and Hormonal.
Minimonommu
__________________
Let's beg n w th alloster c sites. Glycogen synthase is stimulated when the
glucose-6-P is h gh. On the contrary, when the G6P is h gh, it w ll nh bit the
É
Glycogen phosphorylase.
Glycogen phosphorylase is nh bited by many substrates, for example,
1/ ATP, because of the h gh amount of Glycogen converted to Glucose.
2/ ncreased amount of free Glucose (Only n the l ver).
3/ when there is excessive use of ATP, convert it to AMP. (In the muscles) then
the AMP w ll stimulate the enzyme to break down more Glycogen. onlyinliver
É Gly
———————————- PGlucosepATP PGGP
Now let's talk about an important enzyme called Phosphorylase k nase. Th s
enzyme has two states A state wh ch means it's active, and B state, wh ch
means the enzyme is nactive. Th s enzyme is sh ft ng between these states
hormonally.
Was Glycogen
F rstly, there are G-prote n coupled receptors on the membrane of l ver cells.
These receptors respond to spec f c hormones, for example, Glucagon, Ep nephr ne,
and norep nephr ne. When these hormones b nd to the G-prote n, they stimulate the
If phosphorylase Gly
G stimulator. Then, Gs w ll attach to G.T.P. and becomes active. After that, it w ll
stimulate a factor enzyme known as A.C. (Adenylate cyclase) that factor
enzyme is embedded nto the cell membrane. A.C. w ll take ATP and convert it to
cycl c A.M.P. Th s cAMP w ll activate Prote n K nase A (P.K.A.). Then th s P.K.A. w ll Glu
IIpn
phosphorylate (Phosphorylase k nase B) to activate it and convert it to A state.
When the Phosphorylase K nase A is active, it stimulates and phosphorylates the
Glycogen Phosphorylase. Th s w ll start the Glycogenolysis process.
Another G-prote n coupled receptor on the l ver cell b nds w th ep nephr ne and phosphorylase
norep nephr ne. Th s activates Gq. Gq w ll b nd w th G.T.P. and then stimulates
k nase
MjgB
jig
Phosphol pase C embedded on the membrane. P.L.C. w ll break down Phospho nositol
diphosphate (PIP2) nto two molecules, diacylglycerol (D.A.G.) and nositol P
tr phosphate 3 (IP3). IP3 b nds to a receptor on E.R. and pushes out calc um
ATP
The two key enzymes n glycogen metabol sm are:
1. Glycogen synthase for glycogenesis
2. Glycogen phosphorylase for Glycogenolysis.
These two enzymes are regulated n two ways: Alloster c sites and Hormonal.
Minimonommu
__________________
Let's beg n w th alloster c sites. Glycogen synthase is stimulated when the
glucose-6-P is h gh. On the contrary, when the G6P is h gh, it w ll nh bit the
É
Glycogen phosphorylase.
Glycogen phosphorylase is nh bited by many substrates, for example,
1/ ATP, because of the h gh amount of Glycogen converted to Glucose.
2/ ncreased amount of free Glucose (Only n the l ver).
3/ when there is excessive use of ATP, convert it to AMP. (In the muscles) then
the AMP w ll stimulate the enzyme to break down more Glycogen. onlyinliver
É Gly
———————————- PGlucosepATP PGGP
Now let's talk about an important enzyme called Phosphorylase k nase. Th s
enzyme has two states A state wh ch means it's active, and B state, wh ch
means the enzyme is nactive. Th s enzyme is sh ft ng between these states
hormonally.
Was Glycogen
F rstly, there are G-prote n coupled receptors on the membrane of l ver cells.
These receptors respond to spec f c hormones, for example, Glucagon, Ep nephr ne,
and norep nephr ne. When these hormones b nd to the G-prote n, they stimulate the
If phosphorylase Gly
G stimulator. Then, Gs w ll attach to G.T.P. and becomes active. After that, it w ll
stimulate a factor enzyme known as A.C. (Adenylate cyclase) that factor
enzyme is embedded nto the cell membrane. A.C. w ll take ATP and convert it to
cycl c A.M.P. Th s cAMP w ll activate Prote n K nase A (P.K.A.). Then th s P.K.A. w ll Glu
IIpn
phosphorylate (Phosphorylase k nase B) to activate it and convert it to A state.
When the Phosphorylase K nase A is active, it stimulates and phosphorylates the
Glycogen Phosphorylase. Th s w ll start the Glycogenolysis process.
Another G-prote n coupled receptor on the l ver cell b nds w th ep nephr ne and phosphorylase
norep nephr ne. Th s activates Gq. Gq w ll b nd w th G.T.P. and then stimulates
k nase
MjgB
jig
Phosphol pase C embedded on the membrane. P.L.C. w ll break down Phospho nositol
diphosphate (PIP2) nto two molecules, diacylglycerol (D.A.G.) and nositol P
tr phosphate 3 (IP3). IP3 b nds to a receptor on E.R. and pushes out calc um
ATP
