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In chemistry, pyrophosphates are phosphorus that contain two phosphorus atoms in a linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate () and tetrasodium pyrophosphate (), among others. Often pyrophosphates are called diphosphates. The parent pyrophosphates are derived from partial or complete neutralization of pyrophosphoric acid. The pyrophosphate bond is also sometimes referred to as a phosphoanhydride bond, a naming convention which emphasizes the loss of water that occurs when two phosphates form a new bond, and which mirrors the nomenclature for anhydrides of carboxylic acids. Pyrophosphates are found in ATP and other nucleotide triphosphates, which are important in biochemistry. The term pyrophosphate is also the name of 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.
At physiological pHs, pyrophosphate exists as a mixture of doubly and singly protonated forms.
Pyrophosphates are generally white or colorless. The alkali metal salts are water-soluble.C.Michael Hogan. 2011. Phosphate. Encyclopedia of Earth. Topic ed. Andy Jorgensen. Ed.-in-Chief C.J.Cleveland. National Council for Science and the Environment. Washington DC They are good complexing agents for metal ions (such as calcium and many transition metals) and have many uses in industrial chemistry. Pyrophosphate is the first member of an entire series of .
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 in which pyrophosphate reacts with the 3′-nucleosidemonophosphate (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 , and is an acid anhydride of phosphate. It is unstable in aqueous solution and hydrolysis into inorganic phosphate:
In the absence of enzymic catalysis, hydrolysis reactions of simple polyphosphates such as pyrophosphate, linear triphosphate, ADP, and ATP normally proceed extremely slowly in all but highly acidic media.
(The 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 PPi hydrolysis, 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 requires two high-energy phosphates, as to reconstitute AMP into ATP requires two phosphorylation reactions.
The plasma concentration of inorganic pyrophosphate has a reference range of 0.58–3.78 Molarity (95% prediction interval).
Osteoblasts also secrete nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) which causes extracellular PPi production, and ANKH which promotes PPi transport out of cells. Deficiencies of NPP1 and ANK result in deficient extracellular PPi concentrations and are clinically associated with metastatic calcification and excessive calcification of bone (manifesting clinically e.g. as Osteophyte).
In particular, various formulations of diphosphates are used to stabilize whipped cream.Ricardo A. Molins, Phosphates in Food, p. 115
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