Pyrophosphate

In chemistry, pyrophosphate is the name of the anion, the salts, and the esters of pyrophosphoric acid. 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 P₂O₇^4-, and is an acid anhydride of phosphate. It is unstable in aqueous solution and rapidly hydrolyzes into inorganic phosphate:

• P₂O₇^4- + H₂O → 2 HPO₄^2-

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 from ATP will require two phosphorylation reactions.

• AMP + ATP → 2 ADP
• 2 ADP + 2 P_i → 2 ATP

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