Glycogen phosphorylase is one of the phosphorylase enzymes. Glycogen phosphorylase catalyzes the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond. Glycogen phosphorylase is also studied as a model protein regulated by both reversible phosphorylation and allosteric effects.
A debranching enzyme is a molecule that helps facilitate the breakdown of glycogen, which serves as a store of glucose in the body, through glucosyltransferase and glucosidase activity. Together with phosphorylases, debranching enzymes mobilize glucose reserves from glycogen deposits in the muscles and liver. This constitutes a major source of energy reserves in most organisms. Glycogen breakdown is highly regulated in the body, especially in the liver, by various hormones including insulin and glucagon, to maintain a homeostatic balance of blood-glucose levels. When glycogen breakdown is compromised by mutations in the glycogen debranching enzyme, metabolic diseases such as Glycogen storage disease type III can result.
Phosphorylase kinase (PhK) is a serine/threonine-specific protein kinase which activates glycogen phosphorylase to release glucose-1-phosphate from glycogen. PhK phosphorylates glycogen phosphorylase at two serine residues, triggering a conformational shift which favors the more active glycogen phosphorylase “a” form over the less active glycogen phosphorylase b.
Myophosphorylase or glycogen phosphorylase, muscle associated (PYGM) is the muscle isoform of the enzyme glycogen phosphorylase and is encoded by the PYGM gene. This enzyme helps break down glycogen into glucose-1-phosphate, so it can be used within the muscle cell. Mutations in this gene are associated with McArdle disease, a glycogen storage disease of muscle.
Phosphofructokinase (PFK) is a kinase enzyme that phosphorylates fructose 6-phosphate in glycolysis.
The catalytic subunit α of protein kinase A is a key regulatory enzyme that in humans is encoded by the PRKACA gene. This enzyme is responsible for phosphorylating other proteins and substrates, changing their activity. Protein kinase A catalytic subunit is a member of the AGC kinase family, and contributes to the control of cellular processes that include glucose metabolism, cell division, and contextual memory. PKA Cα is part of a larger protein complex that is responsible for controlling when and where proteins are phosphorylated. Defective regulation of PKA holoenzyme activity has been linked to the progression of cardiovascular disease, certain endocrine disorders and cancers.
Calcium/calmodulin-dependent protein kinase type II gamma chain is an enzyme that in humans is encoded by the CAMK2G gene.
5'-AMP-activated protein kinase subunit gamma-2 is an enzyme that in humans is encoded by the PRKAG2 gene.
cAMP-dependent protein kinase catalytic subunit beta is an enzyme that in humans is encoded by the PRKACB gene.
Phosphorylase b kinase regulatory subunit alpha, liver isoform is an enzyme that in humans is encoded by the PHKA2 gene.
Calcium/calmodulin-dependent protein kinase type II delta chain is an enzyme that in humans is encoded by the CAMK2D gene.
Phosphorylase b kinase gamma catalytic chain, skeletal muscle isoform is an enzyme that in humans is encoded by the PHKG1 gene.
Protein phosphatase 1 regulatory subunit 3A is an enzyme that in humans is encoded by the PPP1R3A gene.
2-Oxoisovalerate dehydrogenase subunit beta, mitochondrial is an enzyme that in humans is encoded by the BCKDHB gene.
Voltage-gated potassium channel subunit beta-1 is a protein that in humans is encoded by the KCNAB1 gene.
Phosphorylase b kinase regulatory subunit beta is an enzyme that in humans is encoded by the PHKB gene.
Phosphorylase b kinase gamma catalytic chain, testis/liver isoform is an enzyme that in humans is encoded by the PHKG2 gene.
5'-AMP-activated protein kinase subunit gamma-3 is an enzyme that in humans is encoded by the PRKAG3 gene.
Serine/threonine-protein phosphatase 2B catalytic subunit gamma isoform (PP2BC) is an enzyme that in humans is encoded by the PPP3CC gene.
Glycogen phosphorylase, liver form (PYGL), also known as human liver glycogen phosphorylase (HLGP), is an enzyme that in humans is encoded by the PYGL gene on chromosome 14. This gene encodes a homodimeric protein that catalyses the cleavage of alpha-1,4-glucosidic bonds to release glucose-1-phosphate from liver glycogen stores. This protein switches from inactive phosphorylase B to active phosphorylase A by phosphorylation of serine residue 14. Activity of this enzyme is further regulated by multiple allosteric effectors and hormonal controls. Humans have three glycogen phosphorylase genes that encode distinct isozymes that are primarily expressed in liver, brain and muscle, respectively. The liver isozyme serves the glycemic demands of the body in general while the brain and muscle isozymes supply just those tissues. In glycogen storage disease type VI, also known as Hers disease, mutations in liver glycogen phosphorylase inhibit the conversion of glycogen to glucose and results in moderate hypoglycemia, mild ketosis, growth retardation and hepatomegaly. Alternative splicing results in multiple transcript variants encoding different isoforms [provided by RefSeq, Feb 2011].
