Glucose-6-phosphate 542948 208078731 2008-04-25T10:24:55Z Vina-iwbot 727408 robot Adding: [[zh:葡萄糖-6-磷酸]] {{Chembox new |ImageFileL1=Glucose-6-phosphate-skeletal.png |ImageFileR1=Beta-D-glucose-6-phosphate-3D-balls.png |ImageSize= |IUPACName=(3,4,5,6- tetrahydroxytetrahydropyran- 2-yl) methoxyphosphonic acid |OtherNames= |Section1= {{Chembox Identifiers | CASNo=56-73-5 | PubChem=208 | SMILES=C(C1C(C(C(C(O1)O)O)O)O)OP(=O)(O)O | MeSHName=Glucose-6-phosphate }} |Section2= {{Chembox Properties | Formula=C<sub>6</sub>H<sub>13</sub>O<sub>9</sub>P | MolarMass=260.136 | Appearance= | Density= | MeltingPt= | BoilingPt= | Solubility= }} |Section3= {{Chembox Hazards | MainHazards= | FlashPt= | Autoignition= }} }} '''Glucose 6-phosphate''' (also known as '''Robison ester''') is [[glucose]] sugar [[phosphorylated]] on carbon 6. This compound is very common in [[cell (biology)|cells]] as the vast majority of glucose entering a cell will become phosphorylated in this way. Because of its prominent position in cellular chemistry, glucose 6-phosphate has many possible fates within the cell. It lies at the start of two major [[metabolic pathway]]s: *[[Glycolysis]] *[[Pentose phosphate pathway]] In addition to these metabolic pathways, glucose 6-phosphate may also be converted to [[glycogen]] or [[starch]] for storage. This storage is in the [[liver]] and [[muscle]]s in the form of glycogen for most multicellular [[animals]], and in [[intracellular]] starch or glycogen granules for most other organisms. ==Production of glucose 6-phosphate== ===From glucose=== Within a cell, glucose 6-phosphate is produced by phosphorylation of [[glucose]] on the sixth carbon. This is catalyzed by the [[enzyme]] [[hexokinase]] in most cells, and, in higher animals, [[glucokinase]] in certain cells, most notably liver cells. One molecule of [[Adenosine triphosphate|ATP]] is consumed in this reaction. {{Enzymatic Reaction |foward_enzyme=[[Hexokinase]] |reverse_enzyme= |substrate=<small>D</small>-[[Glucose]] |product=α-<small>D</small>-[[Glucose 6-phosphate]] |reaction_direction_(foward/reversible/reverse)=foward |minor_foward_substrate(s)=[[adenosine triphosphate|ATP]] |minor_foward_product(s)=[[adenosine diphosphate|ADP]] |minor_reverse_substrate(s)= |minor_reverse_product(s)= |substrate_image=Glucose_wpmp.png |product_image=Glucose-6-phosphate_wpmp.png }} {{KEGG compound|C00031}} {{KEGG enzyme|2.7.1.1}} {{KEGG compound|C00668}} {{KEGG reaction|R01786}} The major reason for the immediate phosphorylation of glucose is to prevent diffusion out of the cell. The phosphorylation adds a charged [[phosphate]] group so the [[glucose 6-phosphate]] cannot easily cross the [[cell membrane]]. ===From glycogen=== Glucose-6-phosphate is also produced during [[glycogenolysis]] from glucose-1-phosphate, the first product of the breakdown of [[glycogen]] polymers. == Fate 1: Pentose Phosphate Pathway == When the ratio of NADP<sup>+</sup> : NADPH increases, the body realizes it needs to produce more NADPH (a reducing agent for several reactions like fatty acid synthesis and glutathione reduction in [[erythrocytes]]). This will cause the G6P to be dehydrogenated by glucose 6-phosphate dehydrogenase. This reversible reaction is the initial step of the [[pentose phosphate pathway]], which generates the useful cofactor NADPH as well as ribulose 5-phosphate, a carbon source for the synthesis of other molecules. Also, if the body needs nucleotide precursors of DNA for growth and synthesis, G6P will also be dehydrogenated and enter the pentose phosphate pathway. == Fate 2: Glycolysis == If the cell needs energy or carbon skeletons for synthesis then glucose 6-phosphate is targeted for [[glycolysis]]. Glucose 6-phosphate is first isomerized to [[fructose-6-phosphate]] by [[phosphoglucose isomerase]]. {{Enzymatic Reaction |foward_enzyme=[[Phosphoglucose isomerase]] |reverse_enzyme=[[Phosphoglucose isomerase]] |substrate=α-<small>D</small>-[[Glucose 6-phosphate]] |product=β-<small>D</small>-[[Fructose 6-phosphate]] |reaction_direction_(foward/reversible/reverse)=reversible |minor_foward_substrate(s)= |minor_foward_product(s)= |minor_reverse_substrate(s)= |minor_reverse_product(s)= |substrate_image=Glucose-6-phosphate_wpmp.png |product_image=Fructose-6-phosphate_wpmp.png }} {{KEGG compound|C00668}} {{KEGG enzyme|5.3.1.9}} {{KEGG compound|C05345}} {{KEGG reaction|R00771}} This reaction converts glucose 6-phosphate to [[fructose 6-phosphate]] in preparation for phosphorylation to [[Fructose-1,6-bisphosphate]]. The addition of the 2<sup>nd</sup> phosphoryl group to produce Fructose-1,6-bisphosphate is an irreversible step, and so is used to irreversibly target the glucose 6-phosphate breakdown to provide energy for ATP production via [[glycolysis]]. == Fate 3: Storage as Glycogen == If blood glucose levels are high, the body needs a way to store the excess glucose. After being converted to G6P, [[phosphoglucose isomerase|phosphoglucose mutase]] (isomerase) can turn the molecule into glucose-1-phosphate. Glucose-1-phosphate can then be combined with uridine triphosphate (UTP) to form UDP-glucose. This reaction is driven by the hydrolysis of pyrophosphate that is released in the reaction. Now, the activated UDP-glucose can add to a growing glycogen molecule with the help of [[glycogen synthase]]. This is a very efficient storage mechanism for glucose since it costs the body only 1 ATP to store the 1 glucose molecule and virtually no energy to remove it from storage. It is important to note that glucose-6-phosphate is an allosteric activator of glycogen synthase, which makes sense because when the level of glucose is high the body should store the excess glucose as glycogen. On the other hand, glycogen synthase is inhibited when it is phosphorylated by protein kinase during times of high stress or low blood glucose levels (via hormone induction by [[glucagon]] or [[epinephrine|adrenaline]]). When the body needs glucose for energy, [[glycogen phosphorylase]], with the help of an orthophosphate, can cleave away a molecule from the glycogen chain. The cleaved molecule is in the form of glucose-1-phosphate which can be converted into G6P by phosphoglucomutase. Next, the phosphoryl group on G6P can be cleaved by glucose-6-phosphatase so that a free glucose can be formed. This free glucose can pass through membranes and can enter the bloodstream to travel to other places in the body. == Fate 4: Dephosphorylation and Release into Bloodstream == Liver cells possess [[glucose-6-phosphatase]], which removes the phosphate group from glucose-6-phosphate produced during [[glycogenolysis]] or [[gluconeogenesis]]. The free glucose is sent into the bloodstream for uptake by other cells. == References == * {{cite book |last=Berg |first=Jeremy M. |coauthors=Tymoczko, Stryer |title=Biochemistry |year=2002 |edition=5th |publisher=[[W.H. Freeman and Company]] |location=New York |id=ISBN 0-7167-3051-0 | url =http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=stryer.TOC&depth=10}} ==See also== * [[Glucose]] * [[Glycogen]] * [[Glucose 1-phosphate]] * [[Pentose phosphate pathway]] * [[Glucose-6-phosphate dehydrogenase deficiency]] {{Glycolysis}} [[Category:Organophosphates]] [[Category:Monosaccharides]] [[de:Glucose-6-phosphat]] [[fr:Glucose-6-phosphate]] [[it:Glucosio-6-fosfato]] [[he:גלוקוז-6-פוספט]] [[ja:グルコース-6-リン酸]] [[zh:葡萄糖-6-磷酸]]