In chemistry,
pyrophosphate, or
PPi is an anion observed in living systems, usually formed by the
hydrolysis of
ATP into
AMP.
The pyrophosphate anion has the structure P
2O
74-, and is an
acid anhydride of
phosphate. It is unstable in
aqueous solution and rapidly
hydrolyzess into inorganic phosphate:
or in shorthand notation:
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 PPi will cost 2 high energy phosphates, as to reconstitute AMP from ATP will require 2 phosphorylation reactions.
- AMP + ATP → 2 ADP
- 2 ADP + 2 Pi → 2 ATP
In biology, the term
pyrophosphate may also be used as the name of the bond formed by the
condensation of a phosphorylated biological compound with inorganic phosphate. This bond is also referred to as a
high energy phosphate bond.
