Biochem Glycogen metabolism
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Purpose of glycogen stores in:
1) Liver
2) mm -
1) maintain resting glucose
2) generate ATP - Influence of insulin on transport of glucose into hepatic and extrahepatic cells?
- introduction to glucose in mm cell facilitated by hexokinase which is a constitutive enzyme meaning it is not influenced by insulin. hepatic cells take up glucose by glucokinase enzyme which is an inducable enzyme (activated by insulin).
- Hexokinase
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Km=0.01mM
constitutive enzyme
in tissues in general
inhibited by product - Glucokinase
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Km=10mM
induced enzyme
in liver
not inhibited by product (glu-6-P) - What is significance of glucose -6-Phosphate?
- phosphorylating it traps it inside cell
- debrancher enzyme
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Glucagon world
glycogen to G1P.
debrances - glycogen phosphorylase
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Glucagon world
glycogen to G1P
dephosphorylates - Glycogen synthase
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Insulin world
G1P to glycogen
makes glycogen - 4:6 Transferase (branching enzyme)
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Insulin world
G1P to glycogen
branches for packaging in glycogen - what is glycogenin
- protein that controls number of glycosyl units
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Formation of Branches
2 Enzymatic activities -
1) a1-4 glucosidase
2) a1-4:a1-6 transferase -
Debranching
2 Enzymatic activites -
1) a1-4:a1-4 transferase
2) a1-6 glucosidase -
McArldle's disease
1)Enzyme
2)Organ
3)Symptoms
4) problem -
1)muscle glycogen phosphorylase
2) skeletal muscle
3) weakness & cramping w/ excersize
4) can't mobilize glycogen from cell -
Hers
1)Enzyme
2)Organ
3)Symptoms
4) problem -
1) Liver glycogen phosphorylase
2) Liver
3) mild fasting hypoglycemia, hepatomegly
4) can't mobilize glycogen from cell -
Von Gierke's
1)Enzyme
2)Organ
3)Symptoms
4) problem -
1) glucose-6-phosphatase
2) Liver
3) severe hypoglycemia, hepatomegly
4) total block of glucose getting out to organism -
Pompe's
1)Enzyme
2)Organ
3)Symptoms
4) problem -
1) lysosomal a1-4 glucosidase
2) all organs
3) gardiomegaly; hepatomegaly
4) can't dispose of glycogen -
Regulateion of glycogen synthase in
1)liver
2) skeletal mm -
1)+ insulin & glucose
-glucagon & epinephrine
2) + insulin
- epinephrine -
Regulateion of glycogen phosphorylase in
1)liver
2) skeletal mm -
1) + epinephrine & glucagon
- insulin
2) + epinephrine, AMP, & Ca2+ (through calmodulin)
- insulin & ATP -
1) Phosphorylase A
2) Phosphorylase B -
1) Hormonally induced by glucagon, epinephrine, or Ca into glycogen degradation
2) Locally regulated by AMP into glycgoen regulation