Glycogen Metabolism

Glycogen: a polymer of glucose molecules.

Glycogenolysis: the breakdown of glycogen into G-6-P and glucose in the fasted stated. (+ glucagon)


Glycogen Phosphorylase: has two subunits, phosphorylated, (p) and dephosphorylated, (d).

-Catalyzes the the removal of glucose units from the ends of branches.

-Contains Binding Sites For:

substrates (glycogen, Pi)

co-factor (pyridoxal phosphate)

allosteric activator (AMP)

allosteric inhibitors (ATP, glucose, glucose-6-phosphate)

Regulation: complex, to ensure glucose remains stored as glycogen until absolutely required to maintain blood glucose homeostasis or to supply energy to the cell

Whether or not the enzyme is phosphorylated it can exist in a "tense"(inactive) form or a "relaxed" (active) form .

Only high glucose can force the existence of the phosphorylated tense form.

The enzyme can be rapidly activated without undergoing phosphorylation in response to a hormonal signal

Activator: AMP

Inhibitor: ATP, glucose, glucose-6-phosphate

Glycogenesis: the synthesis of glycogen from glucose in the fed state. (+ for the hormone insulin)

Glucosen + 1 = Glycogen


Glycogen Synthase: has two subunits, independent, (i) and dependent, (d) and it's regulation opposes that of glycogen phosphorylase

Glycogen Synthase-i: is independent of glucose-6-phosphate for its activity.

Glycogen Synthase-d: is dependent on glucose-6-phosphate, this is a mechanism for storing glucose when overabundance is signalled by a build-up of glucose-6-phosphate.


© Dr. Noel Sturm 2020

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