pyrophosphate

Ball-and-stick model of the pyrophosphate anion, P₂O₇⁴⁻

In chemistry, the anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. Pyrophosphates were originally prepared by heating phosphates: the prefix pyro- derived from Greek, means "fire" in this context. Pyrophosphates are good complexing agents and have many uses in industrial chemistry. Pyrophosphate is the first member of an entire series of polyphosphates.

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

ATP → AMP + PP_i

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 slowly hydrolyzes into inorganic phosphate:

P₂O₇⁴⁻ + H₂O → 2 HPO₄²⁻

or in biologists' shorthand notation:

PP_i + H₂O → 2 P_i

(This 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 PP_i irreversible, and biochemical reactions coupled to this hydrolysis are irreversible as well.

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

AMP + ATP → 2 ADP

2 ADP + 2 P_i → 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.

See also

• Sodium pyrophosphate
• Calcium pyrophosphate
• Calcium pyrophosphate dihydrate deposition disease

External links

• MeSH Pyrophosphates