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Glycogen Metabolism
Reducing end
**Small amounts of glycogen in red blood cells & kidneyVERY
small amounts of glycogen in certain glial cells and white blood
cells
**
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Glycogen MetabolismGlycogen Breakdown (Glycogenolysis) and
Glycogen Synthesis
Why breakdown glycogen and not lipid to produce glc?
1. Mobilized faster
2. Can be metabolized anaerobically
lycogen breakdownlc units are removed one at a time from the
nonreducing ends by
hosphorolysis
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Glycogen MetabolismGlycogen Breakdown
Remove all the 14 branches and an additional enzyme is recd
to
remove 16
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Glycogen MetabolismGlycogen Breakdown - Glycogen
phosphorylase
First known example of an allosterically regulated enzyme
First enzyme shown to be controlled by reversible
phosphorylation
In muscle:
Resting muscle
During vigorous muscular
activity, epinephrine
triggers phos
Triggers glycogen
breakdown
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Glycogen MetabolismGlycogen Breakdown - Glycogen
phosphorylase
In liver:
Low blood sugar -
glucagon activates
phosphorylase b kinase,initiates release of glc
into blood
phosphorylase kinase
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Glycogen MetabolismGlycogen Breakdown
Fate of glucose 1-phosphate
Muscle / liver
phosphoglucomutase
G1P G6P Glycolysis
If you just need glucose:
Liver
Gluconeogenesis or
glucose 6-phosphatase
Glycogen
G1P
G6P + H2O
Glc + Pi
In brain & muscle:
No gluconeogenesis and no glucose 6-phosphatase so
get glc from gluconeogenesis in liver or from injested glc, both
of
which get delivered through bloodstream
In liver, glycogen is a reservoir of glc, converted into blood
glc that
moves to other tissues
In muscle, glycogen breakdown produces glc that is metabolized
via
glycolysis to provide ATP for muscle contraction
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Glycogen MetabolismGlycogen Synthesis
Want to polymerize glc, need an activated form of glc -
UDP-glucose
Occurs in almost all tissues, especially in liver and muscle
UDP-glucose
pyrophosphorylase
Glycogen synthase
UDP
Glycogen
chain
Glycogen chain + one more glucose residue
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Glycogen Metabolism
lycogen Synthesis
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Glycogen Metabolism
lycogen Synthesis
lycogen synthase cannot initiate ahain - it needs a primer
rotein enzyme glycogeninmakes the
rimer
nce 8 glucose molecules have been
dded, Glycogenin-[glc]8 is a
ubstrate for glycogen synthase
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Glycogen Metabolism
ontrol
ormones reciprocally regulate synthesis and degradation by
controllin
e phosphorylation/dephosphorylation of the key enzymes
lucagon, epinephrine: stimulate phosphorylase & inhibit
synthase
nsulin:inhibit phosphorylase & stimulate synthase
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Glycogen Metabolism
ontrol
ormones reciprocally regulate synthesis and degradation by
controllin
e phosphorylation/dephosphorylation of the key enzymes
lucagon, epinephrine: stimulate phosphorylaseinhibit
synthase
nsulin: inhibit phosphorylase
stmulate synthase
(+)
Glucagon,
epinephrine
(+)
Insulin
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Glycogen Metabolism
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Glycogen Metabolism
Low blood sugar
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Glycogen Metabolism
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Glycogen Metabolism
