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glycogen (starch) synthase
Identifiers
EC number 2.4.1.11
CAS number 9014-56-6
IntEnz IntEnz view
BRENDA BRENDA entry
ExPASy NiceZyme view
KEGG KEGG entry
MetaCyc metabolic pathway
PRIAM profile
PDB structures
Gene Ontology AmiGO / EGO
glycogen synthase 1 (muscle)
Identifiers
Symbol GYS1
Alt. symbols GYS
Entrez 2997
HUGO 4706
OMIM 138570
RefSeq NM_002103
UniProt P13807
Other data
EC number 2.4.1.11
Locus Chr. 19 q13.3
glycogen synthase 2 (liver)
Identifiers
Symbol GYS2
Entrez 2998
HUGO 4707
OMIM 138571
RefSeq NM_021957
UniProt P54840
Other data
EC number 2.4.1.11
Locus Chr. 12 p12.2-11.2

Glycogen synthase (UDP-glucose-glycogen glucosyltransferase') is a glycosyltransferase enzyme (EC 2.4.1.11) that catalyses the reaction of UDP-glucose and (1,4-α-D-glucosyl)n to yield UDP and (1,4-α-D-glucosyl)n+1.

In other words, this enzyme converts excess glucose residues one by one into a polymeric chain for storage as glycogen. Its presence in the bloodstream is highest in the 30 to 60 minutes[1] following intense exercise. It is a key enzyme in glycogenesis.

Contents

Isozymes

In humans, there are two paralogous isozymes of glycogen synthase:

isozyme tissue distribution gene
glycogen synthase 1 muscle and other tissues GYS1[2]
glycogen synthase 2 liver GYS2[3]

The liver enzyme expression is restricted to the liver, whereas the muscle enzyme is widely expressed. Liver glycogen serves as a storage pool to maintain the blood glucose level during fasting, whereas muscle glycogen synthesis accounts for disposal of up to 90% of ingested glucose. The role of muscle glycogen is as a reserve to provide energy during bursts of activity.[4]

Regulation

The reaction is highly regulated by allosteric effectors such as glucose-6-phosphate, by phosphorylation reactions, and indirectly triggered by the hormone insulin, which is secreted by the pancreas. Phosphorylation of glycogen synthase decreases its activity. The enzyme also cleaves the ester bond between the C1 position of glucose and the pyrophosphate of UDP itself.

Pathology

Mutations in the GYS2 gene are associated with glycogen storage disease type 0.[5]

References

  1. ^ Jentjens R, Jeukendrup A (2003). "Determinants of post-exercise glycogen synthesis during short-term recovery". Sports Med 33 (2): 117–44. PMID 12617691. 
  2. ^ Browner MF, Nakano K, Bang AG, Fletterick RJ (March 1989). "Human muscle glycogen synthase cDNA sequence: a negatively charged protein with an asymmetric charge distribution". Proceedings of the National Academy of Sciences of the United States of America 86 (5): 1443–7. PMID 2493642. PMC 286712. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=2493642. 
  3. ^ Westphal SA, Nuttall FQ (February 1992). "Comparative characterization of human and rat liver glycogen synthase". Archives of biochemistry and biophysics 292 (2): 479–86. PMID 1731614. 
  4. ^ Kollberg G, Tulinius M, Gilljam T, Ostman-Smith I, Forsander G, Jotorp P, Oldfors A, Holme E (October 2007). "Cardiomyopathy and exercise intolerance in muscle glycogen storage disease 0". The New England journal of medicine 357 (15): 1507–14. doi:10.1056/NEJMoa066691. PMID 17928598. 
  5. ^ Orho M, Bosshard NU, Buist NR, Gitzelmann R, Aynsley-Green A, Blümel P, Gannon MC, Nuttall FQ, Groop LC (August 1998). "Mutations in the liver glycogen synthase gene in children with hypoglycemia due to glycogen storage disease type 0". The Journal of clinical investigation 102 (3): 507–15. doi:10.1172/JCI2890. PMID 9691087. 

External links

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