Pyrophosphate

Pyrophosphate

Names
Other names Diphosphate or dipolyphosphate
Identifiers
ChEBI	CHEBI:18361 Y
ChemSpider	559142 Y
DrugBank	DB04160 Y
Jmol 3D model	Interactive image
PubChem	644102
InChI InChI=1S/H4O7P2/c1-8(2,3)7-9(4,5)6/h(H2,1,2,3)(H2,4,5,6)/p-4 Y Key: XPPKVPWEQAFLFU-UHFFFAOYSA-J Y InChI=1/H4O7P2/c1-8(2,3)7-9(4,5)6/h(H2,1,2,3)(H2,4,5,6)/p-4 Key: XPPKVPWEQAFLFU-XBHQNQODAI
SMILES [O-]P(=O)([O-])OP(=O)([O-])[O-]
Properties
Chemical formula	P2O74−
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
Infobox references

In chemistry, pyrophosphate is a phosphorus oxyanion. Compounds such as salts and esters are also called pyrophosphates. The group is also called diphosphate or dipolyphosphate, although this should not be confused with two phosphates. 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.

Chemistry

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.

The synthesis of tetraethyl pyrophosphate was first described in 1854 by Philippe de Clermont at a meeting of the French Academy of Sciences.

In biochemistry

Pyrophosphates are very important in biochemistry. The anion P₂O₇⁴⁻ is abbreviated PP_i and is formed by the hydrolysis of ATP into AMP in cells.

ATP → AMP + PP_i

For example, when a nucleotide is incorporated into a growing DNA or RNA strand by a polymerase, pyrophosphate (PP_i) 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 P₂O₇⁴⁻, and is an acid anhydride of phosphate. It is unstable in aqueous solution and hydrolyzes into inorganic phosphate:

P₂O₇⁴⁻ + H₂O → 2 HPO₄²⁻

or in biologists' shorthand notation:

PP_i + H₂O → 2 P_i

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 PP_i irreversible, and biochemical reactions coupled to this hydrolysis are irreversible as well.

PP_i 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 PP_i into ECF. ANK is a nonenzymatic plasma-membrane PP_i channel that supports extracellular PP_i levels. Defective function of the membrane PP_i channel ANK is associated with low extracellular PP_i and elevated intracellular PP_i. Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) may function to raise extracellular PP_i.

From the standpoint of high energy phosphate accounting, the hydrolysis of ATP to AMP and PP_i requires two high-energy phosphates, as to reconstitute AMP into ATP requires two phosphorylation reactions.

AMP + ATP → 2 ADP

2 ADP + 2 P_i → 2 ATP

The plasma concentration of inorganic pyrophosphate has a reference range of 0.58-3.78 µM (95% prediction interval).

See also

• Adenosine monophosphate
• Adenosine diphosphate
• Adenosine triphosphate
• ATPase
• ATP hydrolysis
• ATP synthase
• Biochemistry
• Bone
• Calcium pyrophosphate
• Calcium pyrophosphate dihydrate deposition disease
• Catalysis
• DNA
• High energy phosphate
• Inorganic pyrophosphatase
• Nucleoside triphosphate
• Nucleotide
• Organophosphate
• Oxidative phosphorylation
• Phosphate
• Phosphoric acid
• Phosphoric acids and phosphates
• RNA
• Sodium pyrophosphate
• Superphosphate
• Thiamine pyrophosphate
• Tooth
• Zinc pyrophosphate

External links

• Pyrophosphates at the US National Library of Medicine Medical Subject Headings (MeSH)