This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Carbohydrates Degradation → Polysaccharides Degradation → Glycogen Degradation|
|Degradation/Utilization/Assimilation → Polymeric Compounds Degradation → Polysaccharides Degradation → Glycogen Degradation|
Glycogen, a branched polymer of glucose, is a storage molecule whose accumulation is under rigorous control in many cells. Glycogen metabolism increases in response to a wide variety of environmental stresses, including heat stress or exposure to sodium chloride, hydrogen peroxide, copper sulfate, high levels of ethanol, or weak organic acids, such as sorbate or benzoate. Glycogen metabolism also increases in response to conditions of nutrient starvation, such as limited nitrogen, carbon, phosphorous, or sulfur, and during diauxic growth on glucose [Francois01].
Glycogen is highly branched. It is formed of small chains of 8 to 12 glucose molecules linked together by α (1->4) bonds (these short linear chains are also called maltodextrins) that are in turn linked to each other by α (1->6) bonds, known as branch linkages.
Glycogen is degraded by two enzyme working in tandem - glycogen phosphorylase and glycogen debranching enzyme (encoded in Saccharomyces cerevisiae by GPH1 and GDB1, respectively [Francois01]). GPH1 progressively releases α-D-glucose 1-phosphate from the linear α-(1,4)-glucosidic bonds [Hwang89, Lerch75], but is not able to break bonds that are close to α(1,6)-branch linkages [Francois01]. The highly-branched, short-chained product formed by exhausetive hydrolysis by glycogen phosphorylase has been named a limit dextrin, since it is the limit of what this enzyme is able to achieve on its own.
The branches are resolved by the dual-functional glycogen debranching enzyme, which eliminates branch points in a two-step process. The first step is the transfer of a maltotriosyl (or maltosyl) unit from a branch to an adjacent α-1,4-glucosyl chain, resulting in formation of a limit dextrin with short branches, catalyzed by the 4-α-glucanotransferase activity (EC 184.108.40.206) of the enzyme. This is followed by the hydrolysis of the residual α-1,6-linked glucose residue by the amylo-α-1,6-glucosidase activity (EC 220.127.116.11) [Teste00]. Once all the branches are removed, the polymer becomes a debranched limit dextrin, and glycogen phosphorylase can resume its activity, resulting in complete breakdown to α-D-glucose 1-phosphate units [Francois01].
Under sporulation conditions, a different yeast enzyme, glucoamylase (encoded by SGA1), can catalyze the final step, producing β-D-glucose instead of the α-D-glucose 1-phosphate produced by glycogen phosphorylase. This enzyme is capable of degrading glycogen, starch, maltotriose, and maltose into glucose [Pugh89]. The role of glycogen degradation during sporulation is not fully understood, since approximately 90% of all SGA1 homozygous null mutants are still able to produce viable spores [Francois01].
Subpathways: glycogenolysis II
Variants: glycogen degradation I
Accorsi89: Accorsi A, Piatti E, Piacentini MP, Gini S, Fazi A (1989). "Isoenzymes of phosphoglucomutase from human red blood cells: isolation and kinetic properties." Prep Biochem 19(3);251-71. PMID: 2533352
Alonso-Casajus et al., 2006: Alonso-Casajus N, Dauvillee D, Viale AM, Munoz FJ, Baroja-Fernandez E, Moran-Zorzano MT, Eydallin G, Ball S, Pozueta-Romero J (2006). "Glycogen phosphorylase, the product of the glgP Gene, catalyzes glycogen breakdown by removing glucose units from the nonreducing ends in Escherichia coli." J Bacteriol 188(14);5266-72. PMID: 16816199
Arrese95: Arrese EL, Rojas-Rivas BI, Wells MA (1995). "Purification and properties of glycogen phosphorylase from the fat body of larval Manduca sexta." Insect Biochem Mol Biol 25(2);209-16. PMID: 7711751
Bao96: Bao Y, Dawson TL, Chen YT (1996). "Human glycogen debranching enzyme gene (AGL): complete structural organization and characterization of the 5' flanking region." Genomics 38(2);155-65. PMID: 8954797
Bao97: Bao Y, Yang BZ, Dawson TL, Chen YT (1997). "Isolation and nucleotide sequence of human liver glycogen debranching enzyme mRNA: identification of multiple tissue-specific isoforms." Gene 197(1-2);389-98. PMID: 9332391
Boeck96: Boeck B, Schinzel R (1996). "Purification and characterisation of an alpha-glucan phosphorylase from the thermophilic bacterium Thermus thermophilus." Eur J Biochem 239(1);150-5. PMID: 8706700
Burwinkel98: Burwinkel B, Bakker HD, Herschkovitz E, Moses SW, Shin YS, Kilimann MW (1998). "Mutations in the liver glycogen phosphorylase gene (PYGL) underlying glycogenosis type VI." Am J Hum Genet 62(4);785-91. PMID: 9529348
Carty75: Carty TJ, Tu J-I , Graves DJ (1975). "Regulation of glycogen phosphorylase. Role of the peptide region surrounding the phosphoserine residue in determining enzyme properties." J Biol Chem 250(13);4980-5. PMID: 1150650
Chang98: Chang S, Rosenberg MJ, Morton H, Francomano CA, Biesecker LG (1998). "Identification of a mutation in liver glycogen phosphorylase in glycogen storage disease type VI." Hum Mol Genet 7(5);865-70. PMID: 9536091
Chen87: Chen YT, He JK, Ding JH, Brown BI (1987). "Glycogen debranching enzyme: purification, antibody characterization, and immunoblot analyses of type III glycogen storage disease." Am J Hum Genet 41(6);1002-15. PMID: 2961257
Cheng07: Cheng A, Zhang M, Gentry MS, Worby CA, Dixon JE, Saltiel AR (2007). "A role for AGL ubiquitination in the glycogen storage disorders of Lafora and Cori's disease." Genes Dev 21(19);2399-409. PMID: 17908927
Diaz-Mejia et al., 2009: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Dombradi86: Dombradi V, Matko J, Kiss Z, Kiss L, Friedrich P, Bot G (1986). "Structural and functional properties of Drosophila melanogaster phosphorylase: comparison with the rabbit skeletal muscle enzyme." Comp Biochem Physiol B 84(4);537-43. PMID: 3093145
Eydallin07: Eydallin G, Viale AM, Moran-Zorzano MT, Munoz FJ, Montero M, Baroja-Fernandez E, Pozueta-Romero J (2007). "Genome-wide screening of genes affecting glycogen metabolism in Escherichia coli K-12." FEBS Lett 581(16);2947-53. PMID: 17543954
Fazi90: Fazi A, Piacentini MP, Piatti E, Accorsi A (1990). "Purification and partial characterization of the phosphoglucomutase isozymes from human placenta." Prep Biochem 20(3-4);219-40. PMID: 2149596
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