Glycogen phosphorylase
| Glycogen phosphorylase | ||
|---|---|---|
| Mass / length primary structure | 842/846/841 amino acids | |
| Secondary to quaternary structure | Dimer with two homodimers | |
| Cofactor | Pyridoxal phosphate | |
| Isoforms | Brain, Liver, Muscle | |
| Identifier | ||
| Gene name (s) | PYGB , PYGL , PYGM | |
| Enzyme classification | ||
| EC, category | 2.4.1.1 , glycosyl transferase | |
| Response type | Splitting off and transfer of a glucose residue to phosphate | |
| Substrate | (1,4-α-D-glucosyl) n + phosphate | |
| Products | (1,4-α-D-glucosyl) n-1 + α-D-glucose-1-phosphate | |
| Occurrence | ||
| Parent taxon | Creature | |
The glycogen phosphorylase (PYG) (more precisely: 1,4-α- D -glucan-phosphate-α- D -glucosyltransferase ) is a cytosolic enzyme of the glycogen metabolism , which catalyzes the phosphorolytic cleavage of the glycogen into glucose-1-phosphate . It occurs in the sub-forms PYGB ( brain , heart ), PYGM ( muscle ) and PYGL ( liver ).
background
The sugar glucose is a central molecule in energy metabolism and the biosynthetic precursor of a large number of biologically important compounds, including non-essential amino acids , fatty acids and the like. a. Glycogen is a polymer made of glucose units and serves the animal organism as a storage form for glucose, similar to the starch in plants. The catalytic activity of glycogen phosphorylase is required to mobilize glucose from the glycogen storage molecule .
Structure and properties
Glycogen phosphorylase is a homodimer with a monomer mass of 97 kDa (human). There are three isoforms, the brain (BB), muscle (MM) and liver (LL) glycogen phosphorylase. All isoenzymes require pyridoxal phosphate for their activity . The K M values for glycogen are in the upper μM to lower mM range. The glycogen phosphorylase is inhibited by glucose and activated by AMP, the extent of the effector action being dependent on the isoform. The specific activity is in the range of a few tens of U / mg protein .
Genetic diseases
Gene defects in the muscle isoform of glycogen phosphorylase lead to McArdle's disease . Mutations in the liver isoform can lead to Hers disease. No corresponding disease is known for the brain isoform.
Glycogen phosphorylase BB
The Glykogenphophorylase BB (GPBB) , is one of the isoforms of glycogen phosphorylase and is used in medical diagnostics.
The glycogen phosphorylase BB occurs in the brain and in high concentrations in the heart muscles . In ischemia , activation of the GPBB results in increased glycogen breakdown . The released GPBB enters the bloodstream within a short time . As a result, GPBB can be used as a biomarker (especially as an earlier "heart attack marker") in the laboratory diagnosis of myocardial infarction .
literature
- Berg / Tymoczko / Stryer: Biochemistry . 5th edition. Spectrum Akademischer Verlag, Heidelberg 2003, ISBN 3-8274-1303-6
Web links
| This text is based in whole or in part on the entry GPBB in Flexikon , a wiki from DocCheck . The takeover took place on July 27, 2010 under the then valid GNU license for free documentation . |