Pyrophosphate

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Editor-In-Chief: Henry A. Hoff

File:Pyrophosphate-3D-balls.png
Ball-and-stick model of the pyrophosphate anion, P2O74−

In chemistry, the anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. The anion P2O74− is abbreviated PPi and is formed by the hydrolysis of ATP into AMP in cells.

  • ATP + H2O <=> 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 where 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 in the absence of enzymic catalysis hydrolyzes extremely slowly into inorganic phosphate in all but highly acidic media:[1]

  • P2O74− + H2O → 2 HPO42−

or in shorthand notation:

  • PPi + H2O → 2 Pi

Enzyme EC 3.6.1.1 catalyzes this hydrolysis.[2] Specificity varies with the source and with the activating metal ion, e.g. Mg2+.[2]

Human GeneID: 5464 PPA1; pyrophosphatase (inorganic) 1 (EC: 3.6.1.1); K01507 inorganic pyrophosphatase [EC: 3.6.1.1]

Human GeneID: 27068 PPA2; pyrophosphatase (inorganic) 2 (EC:3.6.1.1); K01507 inorganic pyrophosphatase [EC: 3.6.1.1]

Human GeneID: 64077 LHPP; phospholysine phosphohistidine inorganic pyrophosphate phosphatase (EC: 3.6.1.1); K11725 phospholysine phosphohistidine inorganic pyrophosphate phosphatase [EC: 3.6.1.1, EC: 3.1.3.-]

Human GeneID: 89797 NAV2; neuron navigator 2 (EC: 3.6.1.1).

This hydrolysis to inorganic phosphate effectively renders the cleavage of ATP to AMP and PPi ultimately irreversible, and biochemical reactions coupled to this hydrolysis are irreversible as well, unless EC 3.6.1.1 is present. EC 3.6.1.1 can reverse the hydrolysis.[2]

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

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

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

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.

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. Unknown parameter |month= ignored (help)
  2. 2.0 2.1 2.2 "NiceZyme View of ENZYME: EC 3.6.1.1".

See also

External links

de:Diphosphate


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