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Pyrophosphate

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Pyrophosphate
Pyrophosphate anion
Names
Other names Diphosphate
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
DrugBank
E number E450 (thickeners, ...)
PubChem CID
InChI
  • InChI=1S/H4O7P2/c1-8(2,3)7-9(4,5)6/h(H2,1,2,3)(H2,4,5,6)/p-4Key: XPPKVPWEQAFLFU-UHFFFAOYSA-J
  • InChI=1/H4O7P2/c1-8(2,3)7-9(4,5)6/h(H2,1,2,3)(H2,4,5,6)/p-4Key: XPPKVPWEQAFLFU-XBHQNQODAI
SMILES
  • P(=O)()OP(=O)()
Properties
Chemical formula P2O7
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). checkY verify (what is  ?) Infobox references
Chemical compound

In chemistry, the anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. Any salt or ester containing two phosphate groups is called a diphosphate. As a food additive, diphosphates are known as E450.

Chemistry

Pyrophosphates were originally prepared by heating phosphates (pyro- from the Greek, meaning fire). Pyrophosphates are good complexing agents 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 esters formed by the condensation of a phosphorylated biological compound with inorganic phosphate as for 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 Philip de Clermount at a meeting of the French Academy of Sciences.

In biochemistry

Main article: Biochemistry

Pyrophosphates are very important in biochemistry. The anion P2O7 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 P2O7, and is an acid anhydride of phosphate. It is unstable in aqueous solution and hydrolyzes into inorganic phosphate:

P2O7 + H2O → 2 HPO4

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.

(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). Cells may channel intracellular PPi into ECF. ANK is a nonenzymatic plasma-membrane PPi channel that supports extracellular PPi levels. Defective function of the membrane PPi channel ANK is associated with low extracellular PPi and elevated intracellular PPi. Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) may function to raise extracellular PPi.

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

See also

References

  1. Huebner PWA, Milburn RM (1980). "Hydrolysis of pyrophosphate to orthophosphate promoted by cobalt(III). Evidence for the role of polynuclear species". Inorg Chem. 19 (5): 1267–72. doi:10.1021/ic50207a032. {{cite journal}}: Unknown parameter |month= ignored (help)
  2. ^ Ho AM, Johnson MD, Kingsley DM (2000). "Role of the mouse ank gene in control of tissue calcification and arthritis". Science. 289 (5477): 265–70. doi:10.1126/science.289.5477.265. PMID 10894769. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  3. ^ Rutsch F, Vaingankar S, Johnson K, Goldfine I, Maddux B, Schauerte P, Kalhoff H, Sano K, Boisvert WA, Superti-Furga A, Terkeltaub R (2001). "PC-1 nucleoside triphosphate pyrophosphohydrolase deficiency in idiopathic infantile arterial calcification". Am J Pathol. 158 (2): 543–54. doi:10.1016/S0002-9440(10)63996-X. PMC 1850320. PMID 11159191. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)

Further reading

  • Schröder HC, Kurz L, Muller WEG, Lorenz B (2000). "Polyphosphate in bone" (PDF). Biochemistry (Moscow). 65 (3): 296–303. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)

External links

Phosphorus compounds
Phosphides
Other compounds
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