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In chemistry, the anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. Any salt or ester containing two phosphate groups is called a diphosphate. As a food additive, diphosphates are known as E450. As well as the normal pyrophosphates, a number of hydrogen pyrophosphates also exist, such as Na2H2P2O7.
Pyrophosphates were originally prepared by heating phosphates (pyro from the Greek, meaning "fire"). Pyrophosphates generally exhibit the highest solubilities among the phosphates; moreover, 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 polyphosphates.
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.
- ATP → AMP + PPi
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'-nucleotidemonophosphate (NMP or dNMP), which is removed from the oligonucleotide to release the corresponding triphosphate (dNTP from DNA, or NTP from RNA).
- P2O74− + H2O → 2 HPO42−
or in biologists' shorthand notation:
- PPi + H2O → 2 Pi
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 irreversible, and biochemical reactions coupled to this hydrolysis are irreversible as well.
PPi occurs in synovial fluid, blood plasma, and urine at levels sufficient to block calcification and may be a natural inhibitor of hydroxyapatite formation in extracellular fluid (ECF). Cells may channel intracellular PPi into ECF. ANK is a nonenzymatic plasma-membrane PPi channel that supports extracellular PPi levels. Defective function of the membrane PPi channel ANK is associated with low extracellular PPi and elevated intracellular PPi. Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) may function to raise extracellular PPi.
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.
- AMP + ATP → 2 ADP
- 2 ADP + 2 Pi → 2 ATP
- Adenosine monophosphate
- Adenosine diphosphate
- Adenosine triphosphate
- ATP hydrolysis
- ATP synthase
- Calcium pyrophosphate
- Calcium pyrophosphate dihydrate deposition disease
- High energy phosphate
- Inorganic pyrophosphatase
- Nucleoside triphosphate
- Oxidative phosphorylation
- Phosphoric acid
- Phosphoric acids and phosphates
- Sodium pyrophosphate
- Thiamine pyrophosphate
- Zinc pyrophosphate
- 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
- Huebner PWA, Milburn RM (May 1980). "Hydrolysis of pyrophosphate to orthophosphate promoted by cobalt(III). Evidence for the role of polynuclear species". Inorg Chem. 19 (5): 1267–72. doi:10.1021/ic50207a032.
- Ho AM, Johnson MD, Kingsley DM (Jul 2000). "Role of the mouse ank gene in control of tissue calcification and arthritis". Science. 289 (5477): 265–70. doi:10.1126/science.289.5477.265. PMID 10894769.
- Rutsch F, Vaingankar S, Johnson K, Goldfine I, Maddux B, Schauerte P, Kalhoff H, Sano K, Boisvert WA, Superti-Furga A, Terkeltaub R (Feb 2001). "PC-1 nucleoside triphosphate pyrophosphohydrolase deficiency in idiopathic infantile arterial calcification". Am J Pathol. 158 (2): 543–54. doi:10.1016/S0002-9440(10)63996-X. PMC 1850320. PMID 11159191.
- Schröder HC, Kurz L, Muller WEG, Lorenz B (Mar 2000). "Polyphosphate in bone". Biochemistry (Moscow). 65 (3): 296–303.
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