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Glycogenolysis
 
 
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Glycogenolysis (also known as "Glycogenlysis") is the catabolism
Catabolism

Catabolism is the set of metabolic pathways which break down molecules into smaller units and release energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides and amino acids, respectively....
 of glycogen
Glycogen

Glycogen is a polysaccharide of glucose which functions as the secondary short term energy storage in animal cells. It is made primarily by the liver and the muscles, but can also be made by the brain and stomach....
 by removal of a glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 monomer through cleavage with inorganic phosphate
Phosphate

A phosphate, an inorganic chemical, is a Salt of phosphoric acid. Inorganic phosphates are mining to obtain phosphorus for use in agriculture and industry....
 to produce glucose-1-phosphate
Glucose-1-phosphate

Glucose 1-phosphate is a glucose molecule with a phosphate group on the 1'-carbon....
.






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Glycogen
Glucose 2d Skeletal
Glucose 6 Phosphate Skeletal
Glycogenolysis (also known as "Glycogenlysis") is the catabolism
Catabolism

Catabolism is the set of metabolic pathways which break down molecules into smaller units and release energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides and amino acids, respectively....
 of glycogen
Glycogen

Glycogen is a polysaccharide of glucose which functions as the secondary short term energy storage in animal cells. It is made primarily by the liver and the muscles, but can also be made by the brain and stomach....
 by removal of a glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 monomer through cleavage with inorganic phosphate
Phosphate

A phosphate, an inorganic chemical, is a Salt of phosphoric acid. Inorganic phosphates are mining to obtain phosphorus for use in agriculture and industry....
 to produce glucose-1-phosphate
Glucose-1-phosphate

Glucose 1-phosphate is a glucose molecule with a phosphate group on the 1'-carbon....
. This derivative of glucose is then converted to glucose-6-phosphate
Glucose-6-phosphate

Glucose 6-phosphate is glucose sugar phosphorylated on carbon 6. This compound is very common in cell as the vast majority of glucose entering a cell will become phosphorylated in this way....
, an intermediate in glycolysis
Glycolysis

Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, C3H5O3-....
.

The hormones glucagon
Glucagon

Glucagon is an important hormone involved in carbohydrate metabolism. Produced by the pancreas, it is released when the glucose level in the blood is low , causing the liver to convert stored glycogen into glucose and release it into the bloodstream....
 and epinephrine
Epinephrine

Epinephrine is a hormone and neurotransmitter.Epinephrine increases the "fight or flight" response of the Sympathetic nervous system of the autonomic nervous system....
 stimulate glycogenolysis.

Function

Glycogenolysis transpires in the muscle and liver tissue, where glycogen is stored, as a hormonal response to epinephrine
Epinephrine

Epinephrine is a hormone and neurotransmitter.Epinephrine increases the "fight or flight" response of the Sympathetic nervous system of the autonomic nervous system....
 (e.g., adrenergic stimulation) and/or glucagon
Glucagon

Glucagon is an important hormone involved in carbohydrate metabolism. Produced by the pancreas, it is released when the glucose level in the blood is low , causing the liver to convert stored glycogen into glucose and release it into the bloodstream....
, a pancreatic peptide triggered by low blood glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 concentrations produced in the Alpha cells of the Islets of Langerhans
Islets of Langerhans

The islets of Langerhans are the regions of the pancreas that contain its endocrine cells. Discovered in 1869 by German pathological anatomist Paul Langerhans, the islets of Langerhans constitute approximately 1 to 2% of the mass of the pancreas....
.

  • Liver
    Liver

    The liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, a few of which are detoxification, protein synthesis, and production of biochemicals necessary for digestion....
     (hepatic) cells can consume the glucose-6-phosphate in glycolysis
    Glycolysis

    Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, C3H5O3-....
    , or remove the phosphate group using the enzyme glucose-6-phosphatase and release the free glucose into the bloodstream for uptake by other cells.


  • Muscle
    MUSCLE

    MUSCLE is public domain, multiple sequence alignment software for protein and nucleotide sequences.MUSCLE is integrated into UGENE bioinformatics tool as a plugin....
     cells in humans do not possess glucose-6-phosphatase and hence will not release glucose, but instead use the glucose-6-phosphate in glycolysis
    Glycolysis

    Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, C3H5O3-....
    .


Clinical significance

Parenteral (intravenous) administration of glucagon is a common human medical intervention in diabetic emergencies when sugar cannot be given orally.

Reaction


First step

The overall reaction for the 1st step is:

Glycogen (n residues) + Pi <-----> Glycogen (n-1 residues)+ G1P

Here, glycogen phosphorylase
Glycogen phosphorylase

Glycogen phosphorylase is one of the phosphorylase enzymes . Glycogen phosphorylase catalyzes the rate limiting step in the degradation of glycogen in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond....
 cleaves the bond at the 1 position by substitution of a phosphoryl group. It breaks down glucose polymer at α-1-4 linkages until 4 linked glucoses are left on the branch. (Furthermore, glycogen phosphorylase
Glycogen phosphorylase

Glycogen phosphorylase is one of the phosphorylase enzymes . Glycogen phosphorylase catalyzes the rate limiting step in the degradation of glycogen in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond....
 (EC 2.4.1.1) can be used as a marker enzyme to determine glycogen breakdown. )

Second step

The 2nd step involves the debranching enzyme
Debranching enzyme

A debranching enzyme is a molecule that helps facilitate the breakdown of glycogen....
 that moves the remaining glucose units to another non-reducing end. This results in fewer glucose units available to glycogen phosphorylase. (step 1) The final action of the debranching enzyme leads to the original glucose 1-P connected 1,4 to another branch being released. Known as Geno in short.

Third step

The 3rd and last stage converts G1P (glucose-1-phosphate) to G6P (glucose-6-phosphate) through the enzyme phosphoglucomutase
Phosphoglucomutase

Phosphoglucomutase is an enzyme that transfers a phosphoryl group on a glucose monomer from the 1' to the 6' position in the forward direction or the 6' to the 1' position in the reverse direction....
.

Regulation

The key regulatory enzyme of the process of glycogenolysis is glycogen phosphorylase
Glycogen phosphorylase

Glycogen phosphorylase is one of the phosphorylase enzymes . Glycogen phosphorylase catalyzes the rate limiting step in the degradation of glycogen in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond....
:
  • Phosphorylation --> activation
  • Dephosphorylation --> inhibition


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