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evolution
plants contain two major Pho forms: the plastidial Pho1 or PhoL (low glycogen affinity) encoded by the PHO1 gene and a cytosolic Pho2 or PhoH (high glycogen affinity) encoded by the PHO2 gene
malfunction
mutations that impair glycogen phosphorylase activity leads to McArdle's disease which is characterized by exercise intolerance, muscle fatigue, and cramps. The irreversible inhibition of the enzyme might represent one of the mechanisms that contribute to mercury-dependent muscle toxicity
malfunction
mutations that impair glycogen phosphorylase activity leads to McArdle's disease which is characterized by exercise intolerance, muscle fatigue, and cramps. The irreversible inhibition of the enzyme might represent one of the mechanisms that contribute to mercury-dependent muscle toxicity
malfunction
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mutations that impair glycogen phosphorylase activity leads to McArdle's disease which is characterized by exercise intolerance, muscle fatigue, and cramps. The irreversible inhibition of the enzyme might represent one of the mechanisms that contribute to mercury-dependent muscle toxicity
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metabolism
glycogen degradation and synthesis during the diurnal cycle are mediated by changes in the activities of phosphorylase and glycogen synthase. Phosphorylase is regulated by phosphorylation of Ser14. Only the phosphorylated form of liver phosphorylase (GPa) is catalytically active. Interconversion between GPa and GPb (unphosphorylated) is dependent on the activities of phosphorylase kinase and of phosphorylase phosphatase. The latter comprises protein phosphatase-1 in conjunction with a glycogen-targeting protein (G-subunit) of the PPP1R3 family. Both GPa and phosphorylated glycogen synthase serve as substrates for the catalytic subunit of protein phosphatase-1 in association with G-subunits
metabolism
glycogen phosphorylase is a key enzyme involved in intracellular glycogen catabolism, catalyzing the first step in glycogen degradation. In the diapause, GPase catalyzes glycogen into the closely related molecule, sorbitol. The GPase gene expression is stress-related and might play an important role in Artemia development and metabolism
metabolism
glycogen synthase and glycogen phosphorylase are the two enzymes that control, respectively, the synthesis and degradation of this polysaccharide
metabolism
muscle glycogen phosphorylase is the rate-limiting enzyme of glycogen breakdown in skeletal muscle
metabolism
muscle glycogen phosphorylase is the rate-limiting enzyme of glycogen breakdown in skeletal muscle
metabolism
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muscle glycogen phosphorylase is the rate-limiting enzyme of glycogen breakdown in skeletal muscle
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physiological function
a gene disruption mutant shows a twofold reduction of glycogen phosphorylase activity and an increased glycogen accumulation. The mutant has higher survival rates than the wild type after exposure to starvation, desiccation and osmotic pressure. The mutant is compromised in its biofilm formation ability and shows a decrease in the amount of glucose, accompanied by increases in rhamnose, fucose and ribose in its exopolysaccharides
physiological function
isoform Pho1 may play an important role in recycling glucosyl units from malto-oligosaccharides back into starch synthesis in the developing wheat endosperm. Protein and enzyme activity increase throughout the period of starch synthesis
physiological function
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molecular crowding by 1 M trimethylamine N-oxide stimulates phosphorylase b and phosphorylase kinase combined binding on glycogen particles. Phosphorylase kinase binding to glycogen particles containing adsorbed phosphorylase shows a two-stage character. At the initial stage, limited size particles with hydrodynamic radius of about 220 nm are formed, whereas the second stage is accompanied by linear growth of hydrodynamic radius. Flavin adenine dinucleotide selectively inhibits phosphorylase kinase binding at the second stage, while its binding in the second stage does not involve phosphorylase b
physiological function
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glycogen phosphorylase catalyses the breakdown of glycogen to glucose 1-phosphate. In the liver this is metabolized further to glucose which is then secreted into the bloodstream
physiological function
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glycogen phosphorylase is a rate-limiting enzyme of glycogen degradation
physiological function
the endosperm-specific plastidial alpha-glucan phosphorylase is important for synthesis of short-chain malto-oligosaccharides, it has an essential role during the initiation process of starch biosynthesis during rice seed development
physiological function
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the enzyme is involved in glycogen catabolism
physiological function
all three isoforms of phosphorylase are regulated allosterically by binding of several metabolite effectors and by reversible phosphorylation of Ser14. The phosphorylase exists as an equilibrium of conformational states, represented by the active conformation (relaxed or R-state) and an inactive conformation (Tense or T-state). The R-state has a high affinity for substrates and certain allosteric effectors such as AMP. The T-state has a low affinity for the substrates, glycogen and phosphate. Although GPb is essentially catalytically inactive in the liver, the various allosteric effectors that stabilize the T-state or R-state determine the interconversion of GPa and GPb through altered accessibility of the phospho residue to the catalytic subunit of protein phosphatase-1, PP1c. D-Glucose is the main physiological ligand that promotes conversion of GPa to GPb in liver, conversion of GPa to GPb by PP1c bound to a G-subunit, overview
additional information
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phosphorylase a is produced and isolated utilizing purified phosphorylase b and commercially available phosphorylase kinase
additional information
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structural analysis of molecular elements that govern molecular recognition by the catalytic site of the enzyme with emphasis in the beta-pocket environment, overview
additional information
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the glycogen phosphorylase dimer can exist in either in unphosphorylated glycogen phosphorylase b or phosphorylated glycogen phosphorylase a form depending on hormonal activation of kinase/phosphatase reactions
additional information
despite a high degree of conservation of residues between liver and muscle isoforms in the ligand binding residues at the catalytic and allosteric sites, the kinetic properties of liver phosphorylase differ from the muscle isoform
additional information
modeling of the glycogen phosphorylase b GPb receptor structure using the 2.15 A resolution GPb-N-4-phenylbenzoyl-2-N'-beta-D-glycopyrglycopyranosyl urea crystal complex, PDB ID 2QLN
additional information
the enzyme activity consists of two activities: (i) binding to the glycogen molecule and (ii) phosphorolysis of the non-reducing-end glucose residues. Activity (i) is mainly due to the activities of the two storage sites, which depend on the ionic strength of the medium and are directly inhibited by cyclodextrins. Activity (ii), the total activity of the two catalytic sites, exhibit relatively little ionic strength dependence. Because the combined activity of (i) and (ii) is deduced using glycogen as an assay substrate, the sole activity of (ii) must be measured using small maltooligosyl-substrates