Glucose 6 Phosphate

Information about Glucose 6 Phosphate

Glucose-6-phosphate

IUPAC name	(3,4,5,6- tetrahydroxytetrahydropyran- 2-yl) methoxyphosphonic acid
Identifiers
CAS number	56-73-5
PubChem	208
MeSH	Glucose-6-phosphate
SMILES	C(C1C(C(C(C(O1)O)O)O)O)OP(=O)(O)O
Properties
Molecular formula	C₆H₁₃O₉P
Molar mass	260.136
Except where noted otherwise, data are given for materials in their standard state (at 25 C, 100 kPa)

Glucose 6-phosphate (also known as Robison ester) is glucose sugar phosphorylated on carbon 6. This compound is very common in 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 pathways:

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 muscles 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 ATP is consumed in this reaction.

D-Glucose	Hexokinase		α-D-Glucose 6-phosphate

	ATP	ADP

Compound C00031 at KEGG Pathway Database. Enzyme 2.7.1.1 at KEGG Pathway Database. Compound C00668 at KEGG Pathway Database. Reaction R01786 at KEGG Pathway Database.

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⁺ : 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.

α-D-Glucose 6-phosphate	Phosphoglucose isomerase	β-D-Fructose 6-phosphate





	Phosphoglucose isomerase

Compound C00668 at KEGG Pathway Database. Enzyme 5.3.1.9 at KEGG Pathway Database. Compound C05345 at KEGG Pathway Database. Reaction R00771 at KEGG Pathway Database.

This reaction converts glucose 6-phosphate to fructose 6-phosphate in preparation for phosphorylation to Fructose-1,6-bisphosphate. The addition of the 2^nd 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 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 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

Berg, Jeremy M.; Tymoczko, Stryer (2002). Biochemistry, 5th, New York: W.H. Freeman and Company. ISBN 0-7167-3051-0.

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A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. A chemical formula is also a short way of showing how a chemical reaction occurs.
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Molar mass, symbol M,^[1] is the mass of one mole of a substance (chemical element or chemical compound).^[2] It is a physical property which is characteristic of each pure substance.
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standard state of a material is its state at 1 bar (100 kilopascals exactly). This pressure was changed from 1 atm (101.325 kilopascals) by IUPAC in 1990.^[1] The standard state of a material can be defined at any given temperature, most commonly 25 degrees Celsius,
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Phosphorylation is the addition of a phosphate (PO₄) group to a protein molecule or a small molecule. Another way to define it would be the introduction of a phosphate group into an organic molecule.
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In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. In each pathway a principal chemical is modified by chemical reactions. These reactions are accelerated, more accurately catalyzed, by enzymes.
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Embden-Meyerhof pathway, initially explained by Gustav Embden and Otto Meyerhof. The term can be taken to include alternative pathways, such as the Entner-Doudoroff Pathway. However, glycolysis will be used here as a synonym for the Embden-Meyerhof pathway.
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The pentose phosphate pathway (also called Phosphogluconate Pathway, or Hexose Monophosphate Shunt [HMP shunt]) is a process that serves to generate NADPH and the synthesis of pentose (5-carbon) sugars. There are two distinct phases in the pathway.
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Glycogen is a polysaccharide of glucose (Glc) which functions as the primary short term energy storage in animal cells. It is made primarily by the liver and the muscles, but can also be made by the brain, uterus, and the vagina.
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Starch (CAS# 9005-25-8, chemical formula (C₆H₁₀O₅)_n,^[1]) is a mixture of amylose and amylopectin (usually in 20:80 or 30:70 ratios).
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liver is an organ present in vertebrates and some other animals. It plays a major role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, and detoxification.
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Muscles may refer to:

Muscles, units of the muscular system of the body.
Muscles (musician)

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In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".

It is used in contrast to extracellular (outside the cell). The cell membrane (and, in plants, the cell wall) is the barrier between the two, and chemical composition of
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Enzymes are proteins that catalyze (i.e. accelerate) chemical reactions.^[1] In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products.
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hexokinase is an enzyme that phosphorylates a six-carbon sugar, a hexose, to a hexose phosphate. In most tissues and organisms, glucose is the most important substrate of hexokinases, and glucose-6-phosphate the most important product.
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Glucokinase (EC 2.7.1.2 ) is an enzyme that facilitates phosphorylation of glucose to glucose-6-phosphate. Glucokinase occurs in cells in the liver, pancreas, gut, and brain of humans and most other vertebrates.
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Adenosine 5'-triphosphate (ATP) is a multifunctional nucleotide that is most important as a "molecular currency" of intracellular energy transfer. In this role, ATP transports chemical energy within cells for metabolism.
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Adenosine diphosphate, abbreviated ADP, is a nucleotide. It is an ester of pyrophosphoric acid with the nucleotide adenine. ADP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase adenine.
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