Boron, Walter F.; Boulpaep, Emile L., eds. (2017). Medical Physiology (3rd ed.). Philadelphia, PA: Elsevier. ISBN 978-1-4557-4377-3.
| Glucose 6-phosphatase. | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| EC no. | 3.1.3.9 | ||||||||
| CAS no. | 9001-39-2 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / QuickGO | ||||||||
| |||||||||
The enzyme glucose 6-phosphatase (EC 3.1.3.9, G6Pase; systematic name D-glucose-6-phosphate phosphohydrolase) catalyzes the hydrolysis of glucose 6-phosphate, resulting in the creation of a phosphate group and free glucose:
- D-glucose 6-phosphate + H2O = D-glucose + phosphate
During fasting, adequate levels of blood glucose are assured by glucose liberated from liver glycogen stores by glycogenolysis as well as glucose generated by gluconeogenesis in the liver as well as - to a lesser extent - the kidneys. G6P is the product of both these pathways[1] and must be converted to glucose before it can be exported from the cell into blood by membrane-bound glucose transporters.[2] G6Pase is therefore principally expressed in the liver and kidney[1] - while skeletal muscle collectively contain the most substantial glycogen reserve in the body, glucose cannot be mobilised from it as muscle lacks G6Pase.[3]: 1171
Insulin inhibits hepatic G6Pase activity,[3]: 1046 whereas glucagon promotes it.[3]: 1052 Expression of G6Pase is increased during starvation, in diabetes, and by glucocorticosteroids.[1]
Glucose 6-phosphatase is a complex of multiple component proteins, including transporters for G6P, glucose, and phosphate. The main phosphatase function is performed by the glucose 6-phosphatase catalytic subunit. In humans, there are three isozymes of the catalytic subunit: glucose 6-phosphatase-α, encoded by G6PC; IGRP, encoded by G6PC2; and glucose 6-phosphatase-β, encoded by G6PC3.[4]
Glucose 6-phosphatase-α and glucose 6-phosphatase-β are both functional phosphohydrolases, and have similar active site structure, topology, mechanism of action, and kinetic properties with respect to G6P hydrolysis.[5] In contrast, IGRP has almost no hydrolase activity, and may play a different role in stimulating pancreatic insulin secretion.[6]
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- ^ a b c Van SCHAFTINGEN, Emile; Gerin, Isabelle (15 March 2002). "The glucose-6-phosphatase system". Biochemical Journal. 362 (3): 513–532. doi:10.1042/0264-6021:3620513. PMC 1222414. PMID 11879177.
- ^ Nordlie R, et al. (1985). The Enzymes of biological membranes, 2nd edition. New York: Plenum Press. pp. 349–398. ISBN 0-306-41453-8.
- ^ a b c Boron, Walter F.; Boulpaep, Emile L., eds. (2017). Medical Physiology (3rd ed.). Philadelphia, PA: Elsevier. ISBN 978-1-4557-4377-3.
- ^ Hutton JC, O'Brien RM (October 2009). "Glucose-6-phosphatase catalytic subunit gene family". The Journal of Biological Chemistry. 284 (43): 29241–5. doi:10.1074/jbc.R109.025544. PMC 2785553. PMID 19700406.
- ^ Ghosh A, Shieh JJ, Pan CJ, Chou JY (March 2004). "Histidine 167 is the phosphate acceptor in glucose-6-phosphatase-β forming a phosphohistidine enzyme intermediate during catalysis". The Journal of Biological Chemistry. 279 (13): 12479–83. doi:10.1074/jbc.M313271200. PMID 14718531.
- ^ Shieh JJ, Pan CJ, Mansfield BC, Chou JY (September 2005). "In islet-specific glucose-6-phosphatase-related protein, the β cell antigenic sequence that is targeted in diabetes is not responsible for the loss of phosphohydrolase activity". Diabetologia. 48 (9): 1851–9. doi:10.1007/s00125-005-1848-6. PMID 16012821.