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CHAPTER 24 Glycogen Degradation
Most glycogen is found in muscle and liver cellsGlycogen particles in a liver cell section
The enzyme Glycogen Phosphorylase- Catalyzes phosphorolysis – Cleavage of a bond by group
transfer to an oxygen atom of phosphate
- Glycogen phosphorylase removes glucose residues fromthe end of glycogen
- Acts only on a-14 linkages of a glycogen polymer
- The product is glucose 1-phosphate, which is convertedto glucose 6-phosphate
Figure 24.2: The glycogen phosphorylase removes single glucose units via cleavageof a-1,4 glycosidic bonds.
Metabolism of Glucose 1-Phosphate
Phosphoglucomutase catalyzes the conversion of glucose 1-phosphate to glucose 6-phosphate
Phosphogluco-mutase
Phosphogluco-mutase
Phosphogluco-mutase
Hormones Regulate Glycogen Metabolism
- Insulin produced by b-cells of the pancreas in response to high blood glucose (the “fed” state)
- Insulin increases the rate of glucose transport into muscle andadipose tissue via the glucose transporter (GLUT 4)
- Glucagon is secreted by the a-cells of the pancreas in responseto low blood glucose (the fasting state)
- Glucagon stimulates glycogen degradation to restore blood glucose to steady-state levels
- Epinephrine (adrenaline) is released from the adrenal glands in response to sudden energy requirements (“fight or flight”)
Hormones Regulate Glycogen Metabolism
- Epinephrine and glucagon stimulates the breakdown of glycogento glucose 1-phosphate
Figure 24.11: Signal transduction pathway activates glycogen phosphorylase
Amplification viacyclic AMP