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Glucose 6
phosphatase
glucose
G-6-P
F-6-P
fructose 1,6 bis
phosphatase
F-1,6-bisP
DHAP
G-3-P
1,3,bis-PG
3-P-G
2-P-G
1. pyruvate carboxylase
2. phosphoenol pyruvate
carboxy kinase
PEP
Pyruvate
from lactate
from pyruvate
OAA
pyruvate
PEP
pyruvate
Asp
malate
mitochondrial
matrix
cytosol
pyruvate
Asp
malate
pyruvate
lactate
OAA
OAA
alanine
PEP
G3P dehydro
G3P dehydro
glucose
from lactate
pyruvate
from pyruvate
Pyruvate
carboxylase
Pyruvate
carboxylase
malate
NADH dehydrog.
PEPCK
transaminase
NAD
PEP
Asp
malate
OAA
pyruvate
mitochondrial
matrix
cytosol
pyruvate
LDH
NADH
lactate
malate
pyruvate
malate
transaminase
NADHtransaminase
dehydro.
Asp
OAA
OAA
PEPCK
PEPCK
PEP
G3P dehydro
G3P dehydro
glucose
alanine
Cellulose
b1-4 glucose
Plants
Animals
Starch
• amylose
• amylopectin
Glycogen
a1-4 + a1-6 glucose
Structure of Glycogen
A
A
A
A
A
A
A
B
B
A
B
B
B
B
A
A
B
B
B
A
B
B
A
•
•
•
•
B
A
A
A
A
A
each B-chain has two branch points
all chains have the same length of 14 residues
the material is distributed at 50% between A- and B-chains.
a molecule of glycogenin, a protein that acts as a primer, is
located at the centre of the structure.
See also amylopectin:fig 8-24 in Horton
amylopectin
Structure of Glycogen
A
A
A
5
A
A
B
B
3
B
2
1
B
B
B
B
B
A
A
4
A
A
A
B
A
B
B
A
B
A
A
A
A
A
•
•
•
•
each B-chain has two branch points
all chains have the same length of 14 residues
the material is distributed at 50% between A- and B-chains.
a molecule of glycogenin, a protein that acts as a primer, is
located at the centre of the structure.
• because synthesis and degradation takes place at non-reducing
ends, branching provides more sites for these processes occur.
See also amylopectin:fig 8-24 in Horton
amylopectin
After a meal as much as 10% by weight of the liver may
be glycogen
Regulation of glycogen synthase
Allosteric:
G6P
Phosphorylation :
[Gsa] R
active
PKA
PP1
inhibits
[GSb-PO4]T
inactive
G6P
[GSb-PO4]R
active
Phosphorylase cleaves a1-4 bonds from the non-reducing
termini of glycogen to yield Glucose -1-P
Glycogen debranching enzyme
Glycogen degradation: combined action of phosphorylase
and debranching enzyme
a1
6
branching enzyme
a1
6
Glycogen synthesis: glycogen synthase and
branching enzyme
a1-4 linkage
autocatalysis
UDP-glucosyltransferase
autocatalysis
several cycles
glycogen synthase
several cycles
Amylo(1,4 1,6) transglycosylase
(branching enzyme)
a1-6 linkage
glycogen synthase/
branching enzyme
multiple cycles
Regulation of phosphorylase
Allosteric:
AMP (muscle)
G6P, ATP
phosphorylation:
Regulation of phosphorylase: part 2
2ATP
T
AMP
(muscle)
Phos kinase (liver, muscle)
Phos b
inactive
2ADP
2Pi
PP1
PO4
T
G6P
ATP
PO4
Phos a
inactive
R
Phos b
active
glucose
(liver)
PO4
R
PO4
Phos a
active
Co-ordinated regulation of phosphorylase
and glycogen synthase by PKA
GSa
GSb-PO4
active
inactive
PP1
active
PKA
PP1-PO4
inactive
Phos kinaseb
inactive
See fig 13.7 Horton
Phos kinasea-PO4
active
Ca2+
Phosb
Phosa-PO4
inactive
active
Gb,g
G-protein
linked
receptor
Ga
Adenylate
cyclase
GDP
GDP
GTP
GDP
GDP
GTP
GTP
Pi
ATP
GDP
cAMP + PPi
3’5’ cyclic AMP
Adenyl cyclase
ATP
3’5’ cyclic AMP + PPi
Cyclic nucleotide phosphodiesterase
AMP
3’5’ cyclic AMP
Regulation of PKA
R
C
R
C
inactive
4 cAMP
R
R
C
C
active