Glycogen Phosphorylase: Difference between revisions

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Andrea Gorrell, Riley Hicks, Amy Chahal, David Canner, Michal Harel, Alexander Berchansky, Ann Taylor, Joel L. Sussman

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 <StructureSection load='1ygp' size='350' side='right' caption='Yeast glycogen phosphorylase dimer with pyridoxal-5-phosphate and phosphate (PDB entry [[1ygp]])' scene=''>
 =Introduction=
-'''Glycogen phosphorylase''' (GP) catalyzes the hydrolysis of glycogen to generate glucose-1-phosphate  and shortened glycogen molecule and is considered the rate limiting step in the degradation of glycogen<ref name="gp">PMID: 15214781 </ref>. It is a part of the glucosyltransferase family and acts on the α-1,4-glycosidic linkage; the phosphorylase comes to a standstill 4 residues from an α-1,6-branchpoint, where debranching enzyme takes over <ref name =“gp3”> PMID: 11949930</ref>. The glucose-1-phophate is then further degraded via the pathway of glycolysis. Studies have found that mammals have liver, muscle and brain isoforms of phosphorylase but it is found among all species; muscle glycogen phosphorylase is present to degrade glycogen to forms of energy by means of glycolysis during muscle contractions and liver glycogen is present to regulate the blood glucose levels within the blood <ref name =“gp3”/><ref name="PLP">Palm D, Klein HW, Schinzel R, Buehner M, Helmreich EJM. The role of pyridoxal 5’-phosphate in glycogen phosphorylase catalysis. Biochemistry.  1990 Feb 6; 29(5):1099-1107.</ref>.   See also [[Glycogen Metabolism & Gluconeogenesis], [[Glycogenolysis]].
+'''Glycogen phosphorylase''' (GP) catalyzes the hydrolysis of glycogen to generate glucose-1-phosphate  and shortened glycogen molecule and is considered the rate limiting step in the degradation of glycogen<ref name="gp">PMID: 15214781 </ref>. It is a part of the glucosyltransferase family and acts on the α-1,4-glycosidic linkage; the phosphorylase comes to a standstill 4 residues from an α-1,6-branchpoint, where debranching enzyme takes over <ref name =“gp3”> PMID: 11949930</ref>. The glucose-1-phophate is then further degraded via the pathway of glycolysis. Studies have found that mammals have liver, muscle and brain isoforms of phosphorylase but it is found among all species; muscle glycogen phosphorylase is present to degrade glycogen to forms of energy by means of glycolysis during muscle contractions and liver glycogen is present to regulate the blood glucose levels within the blood <ref name =“gp3”/><ref name="PLP">Palm D, Klein HW, Schinzel R, Buehner M, Helmreich EJM. The role of pyridoxal 5’-phosphate in glycogen phosphorylase catalysis. Biochemistry.  1990 Feb 6; 29(5):1099-1107.</ref>.   See also [[Glycogen Metabolism & Gluconeogenesis]], [[Glycogenolysis]].
 '''GP A''' which is usually active is phosphorylated on Ser 14 of each subunit. GP A is the liver isozyme.  '''GP B''' is usually inactive and is the muscle isozyme.  GP B is also  called '''myophosphorylase'''.