Glycogen catabolism (WP478)

Glycogen, a branched polymer of glucose, is a storage molecule whose accumulation is under rigorous control in many cells (CITS: 11152943). 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 (CITS: 11152943). 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 (CITS: 11152943). Under all of the above conditions, glycogen is degraded by Gph1p and Gdb1p enzymes, which are phosphorylase and debranching enzymes respectively (CITS: 11152943). GPH1 progressively releases glucose-1-phosphate from linear alpha (1,4)-glucosidic bonds in glycogen (CITS: 2657401)(CITS: 1092346) but is not able to break alpha (1,4)-glucosidic bonds that are close to alpha (1,6)-branch linkages (CITS: 11152943). The branches are resolved by Gdb1p, which eliminates branch points in a two-step process. The first step of the process is the transfer of a maltotriosyl (or maltosyl) unit from the branch to an adjacent alpha-1,4-glucosyl chain by the oligo-1,4 to 1,4-glucanotransferase activity (EC 2.4.1.25) of Gdb1p (CITS: 11094287). The second step is the subsequent hydrolysis of the residual alpha-1,6-linked glucose residue by the alpha-1,6-glucosidase activity (EC 3.2.1.33) of Gdb1p (CITS: 11094287). Once the branch is resolved, Gph1p can continue glycogen degradation (CITS: 11152943). In sporulating cells, glycogen can also be degraded by Sga1p, which is a glucoamylase enzyme only expressed during late sporulation (CITS: 11152943). SGA1 encodes an amylo (1,4-1,6)-glucosidase (CITS: 11152943) capable of degrading glycogen, starch, maltotriose, and maltose into glucose, with maximum activity against glycogen at pH 5.5 (CITS: 2493265). The role of glycogen degradation during sporulation is not fully understood, since glycogen is rapidly degraded during sporulation in wild-type cells, but approximately 90% of all sga1 homozygous null mutants are able to produce viable spores (CITS: 11152943). Thus far, none of the phenotypes seen in S. cerevisiae glycogen catabolism mutants correspond to the mammalian glycogen storage diseases associated with mutations in human genes involved in glycogen catabolism (CITS: 11152943). SOURCE: SGD pathways, http://pathway.yeastgenome.org/server.html
last edited

Authors

J.Heckman, MaintBot, Christine Chichester, Egonw, DeSl, and Eweitz

Cited In

Organism

Saccharomyces cerevisiae

Communities

Annotations

Pathway Ontology: glycogen degradation pathway

Participants

Label Type Compact Identifier
Maltotetraose Metabolite wikidata:Q27096312
beta-D-Glucose Metabolite chebi:15903
1,4-alpha-D-Glucan Metabolite chebi:15444
glycogens Metabolite chebi:24384
PGM2 GeneProduct sgd:S000004711
maltose Metabolite cas:69-79-4
GDB1 GeneProduct sgd:S000006388
maltodextrin Metabolite cas:9050-36-6
glucose-6-phosphate (closed form) Metabolite chebi:75150
phosphate Metabolite cas:14265-44-2
PGM1 GeneProduct sgd:S000001610
H2O Metabolite chebi:15377
SGA1 GeneProduct ensembl:YIL099W
glycogen(n-1) Metabolite chebi:28087
GPH1 GeneProduct sgd:S000006364
glucose-1-phosphate (closed form) Metabolite chebi:16077
maltotriose Metabolite cas:1109-28-0

References

  1. François J, Parrou JL. Reserve carbohydrates metabolism in the yeast Saccharomyces cerevisiae. FEMS Microbiol Rev. 2001 Jan;25(1):125–45. PubMed Europe PMC Scholia