biochem - usmle_guy

[ArchivalUser]

I mean protein kinase A

[ArchivalUser]

a silly confusion dont mind pls...

kaplan says" Glucagon promotes phosphorylation of Glycogen phosphorylase and Glycogen synthase.....The result is two fold..synthesis slows down,,,degradation increase,,,,How phosphorylation of glycogen synthase slows it down..shouldn't it increase...that's my confusion..

[ArchivalUser]

so it's not necessary that phosphorylation of enzyme increases its activity???????????????????

[ArchivalUser]

ok ,u wanted to mention that it increases the amount of enzimes,didn't u?

[ArchivalUser]

Glycogen Synthase Enzyme:

-Dephosphorylated form----Active
-Phosphorylated form-------Inactive

Insulin*De-phosphorylate via Protein phosphaTASE-1)

tyrosin kinase receptor--->+"Protein phosphatase-1"--->cz Dephosphorylation of Glycogen Synthase (become active)---->Glycogenesis


Glucagon,Epinephrin,Adrenalin*Phosphorylate via Protein Kinase-A)

beta2-receptor(Gs-coupled)--->incr cAMP--->+ "Protein kinase-A"--->cz Phosphorylation of Glycogen Synthase (become Inactive)----->Prevent Glycogenesis

NOTE: opposite is applied to the effect on "Glycogen phosphorylase"(Glycogenolysis)

as this enzyme is
Dephosphorylated form---*Inactive
Phosphorylated form------*Active

***so to make it more simple just remember the ACTIVE forms
G.Synthase----------De-phosphorylated from (Active)
G.Phosphorylase --------Phosphorylated from (Active)

or may be just remember u need "Phosphorylation" to breakdown Glycogen and the other is the other one.

[ArchivalUser]

great explanation...crystal clear...Thank Sarim..