glycogen phosphorylase

Function

• allosteric enzyme in carbohydrate metabolism
• catalyzes formation of glucose-1-phosphate from glycogen during glycogenolysis
• enzymes from different sources differ in their regulatory mechanisms & in their natural substrates
• all known phosphorylases share catalytic & structural properties
• activity of phosphorylase is controlled both by allosteric means (through the noncovalent binding of metabolites) & by covalent modification
• AMP allosterically activates, whereas ATP, ADP, & glucose-6-phosphate allosterically inhibit
• phosphorylation by phosphorylase kinase activates

(1,4-alpha-D-glucosyl)(n)* + phosphate
                    <-->
(1,4-alpha-D-glucosyl)(n-1)* + alpha-D glucose-1-phosphate

* glycogen

Cofactor: pyridoxal phosphate

Pathology

• defects associated with glycogen storage disease type V (McArdle Disease)

Laboratory

• phosphorylase in erythrocytes

More general terms

• phosphotransferase
• hexosyltransferase
• phosphoprotein
• regulatory molecule
• oligomerizing protein

More specific terms

• phosphorylase-A
• phosphorylase-B (brain glycogen phosphorylase, PYGB)
• phosphorylase-L (liver glycogen phosphorylase, PYGL)
• phosphorylase-M (myophosphorylase, muscle glycogen phosphorylase, PYGM)