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Pyrophosphate

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Title: Pyrophosphate  
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Subject: Phosphate, Adenosine monophosphate, Long-chain-fatty-acid—CoA ligase, Urea cycle, DNA ligase
Collection: Anions, Dietary Minerals, Molecular Biology, Nucleotides, Pyrophosphates
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Pyrophosphate

Pyrophosphate
Pyrophosphate anion
Names
Other names
Diphosphate or dipolyphosphate
Identifiers
ChEBI  Y
ChemSpider  Y
DrugBank  Y
Jmol-3D images Image
PubChem
Properties
P2O74−
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 Y  (: Y/N?)

In chemistry, pyrophosphate is a phosphorus oxyanion. Compounds such as salts and esters are also called pyrophosphates. The group is also called diphosphate or dipolyphosphate, although this should not be confused with two phosphates. As a food additive, diphosphates are known as E450. As well as the normal pyrophosphates, a number of hydrogen pyrophosphates also exist, such as Na2H2P2O7.

Contents

  • Chemistry 1
  • In biochemistry 2
  • See also 3
  • References 4
  • Further reading 5
  • External links 6

Chemistry

Pyrophosphates were originally prepared by heating phosphates (pyro from the Greek, meaning "fire"). Pyrophosphates generally exhibit the highest solubilities among the phosphates;[1] moreover, they are good complexing agents for metal ions (such as calcium and many transition metals) and have many uses in industrial chemistry. Pyrophosphate is the first member of an entire series of polyphosphates.

The term pyrophosphate is also the name of dimethylallyl pyrophosphate. This bond is also referred to as a high-energy phosphate bond.

The synthesis of tetraethyl pyrophosphate was first described in 1854 by Philippe de Clermont at a meeting of the French Academy of Sciences.

In biochemistry

Pyrophosphates are very important in biochemistry. The anion P2O74− is abbreviated PPi and is formed by the hydrolysis of ATP into AMP in cells.

ATP → AMP + PPi

For example, when a nucleotide is incorporated into a growing DNA or RNA strand by a polymerase, pyrophosphate (PPi) is released. Pyrophosphorolysis is the reverse of the polymerization reaction in which pyrophosphate reacts with the 3'-nucleotidemonophosphate (NMP or dNMP), which is removed from the oligonucleotide to release the corresponding triphosphate (dNTP from DNA, or NTP from RNA).

The pyrophosphate anion has the structure P2O74−, and is an acid anhydride of phosphate. It is unstable in aqueous solution and hydrolyzes into inorganic phosphate:

P2O74− + H2O → 2 HPO42−

or in biologists' shorthand notation:

PPi + H2O → 2 Pi

In the absence of enzymic catalysis, hydrolysis reactions of simple polyphosphates such as pyrophosphate, linear triphosphate, ADP, and ATP normally proceed extremely slowly in all but highly acidic media.[2]

(The reverse of this reaction is a method of preparing pyrophosphates by heating phosphates.)

This hydrolysis to inorganic phosphate effectively renders the cleavage of ATP to AMP and PPi irreversible, and biochemical reactions coupled to this hydrolysis are irreversible as well.

PPi occurs in synovial fluid, blood plasma, and urine at levels sufficient to block calcification and may be a natural inhibitor of hydroxyapatite formation in extracellular fluid (ECF).[3] Cells may channel intracellular PPi into ECF.[4] ANK is a nonenzymatic plasma-membrane PPi channel that supports extracellular PPi levels.[4] Defective function of the membrane PPi channel ANK is associated with low extracellular PPi and elevated intracellular PPi.[3] Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) may function to raise extracellular PPi.[4]

From the standpoint of high energy phosphate accounting, the hydrolysis of ATP to AMP and PPi requires two high-energy phosphates, as to reconstitute AMP into ATP requires two phosphorylation reactions.

AMP + ATP → 2 ADP
2 ADP + 2 Pi → 2 ATP

The plasma concentration of inorganic pyrophosphate has a reference range of 0.58-3.78 µM (95% prediction interval).[5]

See also

References

  1. ^ C.Michael Hogan. 2011. . Encyclopedia of Earth. Topic ed. Andy Jorgensen. Ed.-in-Chief C.J.Cleveland. National Council for Science and the Environment. Washington DCPhosphate
  2. ^ Van Wazer JR, Griffith EJ, McCullough JF (Jan 1955). "Structure and Properties of the Condensed Phosphates. VII. Hydrolytic Degradation of Pyro- and Tripolyphosphate". J. Am. Chem. Soc. 77 (2): 287–291.  
  3. ^ a b Ho AM, Johnson MD, Kingsley DM (Jul 2000). "Role of the mouse ank gene in control of tissue calcification and arthritis". Science. 289 (5477): 265–70.  
  4. ^ a b c Rutsch F, Vaingankar S, Johnson K, Goldfine I, Maddux B, Schauerte P, Kalhoff H, Sano K, Boisvert WA, Superti-Furga A, Terkeltaub R (Feb 2001). "PC-1 nucleoside triphosphate pyrophosphohydrolase deficiency in idiopathic infantile arterial calcification". Am J Pathol. 158 (2): 543–54.  
  5. ^ Ryan LM, Kozin F, McCarty DJ (1979). "Quantification of human plasma inorganic pyrophosphate. I. Normal values in osteoarthritis and calcium pyrophosphate dihydrate crystal deposition disease". Arthritis Rheum. 22 (8): 886–91.  

Further reading

  • Schröder HC, Kurz L, Muller WEG, Lorenz B (Mar 2000). "Polyphosphate in bone" (PDF). Biochemistry (Moscow). 65 (3): 296–303. 

External links

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