Pyrophosphate

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In chemistry, the anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. 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 rapidly hydrolyzes into inorganic phosphate:

• P₂O₇⁴⁻ + H₂O → 2 HPO₄²⁻

or in shorthand notation:

• PP_i + H₂O → 2 P_i

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 dihydrate deposition disease