Pyrophosphate

Encyclopedia : P : PY : PYR : Pyrophosphate

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

ATP → AMP + PP_i

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.

Pyrophosphate

See also