polyphosphate

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      A polyphosphate is a salt or ester of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic (also called, ring) structures. In biology, the polyphosphate esters ADP and ATP are involved in energy storage. A variety of polyphosphates find application in mineral sequestration in municipal waters, generally being present at 1 to 5 ppm. GTP, CTP, and UTP are also nucleotides important in the protein synthesis, lipid synthesis, and carbohydrate metabolism, respectively.
      Polyphosphates are also used as food additives, marked E452.


      Structure




















      The structure of tripolyphosphoric acid illustrates the principles which define the structures of polyphosphates. It consists of three tetrahedral PO4 units linked together by sharing oxygen centres. For the linear chains, the end phosphorus groups share one oxide and the others phosphorus centres share two oxide centres. The corresponding phosphates are related to the acids by loss of the acidic protons. In the case of the cyclic trimer each tetrahedron shares two vertices with adjacent tetrahedra.
      Sharing of three corners is possible. This motif represents crosslinking of the linear polymer. Crosslinked polyphosphates adopt the sheet-structure Phyllosilicates, but such structures occur only under extreme conditions.


      Formation and synthesis


      Polyphosphates arise by polymerization of phosphoric acid derivatives. The process begins with two phosphate units coming together in a condensation reaction.

      2 H(PO4)2− ⇌ (P2O7)4− + H2O
      The condensation is shown as an equilibrium because the reverse reaction, hydrolysis, is also possible. The process may continue in steps; at each step another (PO3)− unit is added to the chain, as indicated by the part in brackets in the illustration of polyphosphoric acid. P4O10 can be seen as the end product of condensation reactions, where each tetrahedron shares three corners with the others. Conversely, a complex mix of polymers is produced when a small amount of water is added to phosphorus pentoxide.


      Acid-base and complexation properties


      Polyphosphates are weak bases. A lone pair of electrons on an oxygen atom can be donated to a hydrogen ion (proton) or a metal ion in a typical Lewis acid-Lewis base interaction. This has profound significance in biology. For instance, adenosine triphosphate is about 25% protonated in aqueous solution at pH 7.

      ATP4− + H+ ⇌ ATPH3−, pKa



      ≈


      {\displaystyle \approx }

      6.6
      Further protonation occurs at lower pH values.


      The "high energy" phosphate bond


      ATP forms chelate complexes with metal ions. The stability constant for the equilibrium

      ATP4− + Mg2+ ⇌ MgATP2−, log β



      ≈


      {\displaystyle \approx }

      4
      is particularly large. The formation of the magnesium complex is a critical element in the process of ATP hydrolysis, as it weakens the link between the terminal phosphate group and the rest of the molecule.
      The energy released in ATP hydrolysis,

      ATP4− + H2O → ADP3− + Pi−
      at ΔG



      ≈


      {\displaystyle \approx }

      -36.8 kJ mol−1 is large by biological standards. Pi stands for inorganic phosphate, which is protonated at biological pH. However, it is not large by inorganic standards. The term "high energy" refers to the fact that it is high relative to the amount of energy released in the organic chemical reactions that can occur in living systems.


      High-polymeric inorganic polyphosphates


      High molecular weight polyphosphates are well known. One derivative is the glassy (i.e., amorphous) Graham's salt. Crystalline high molecular weight polyphosphates include Kurrol’s salt and Maddrell’s salt (white powder practically insoluble in water). These species have the formula [NaPO3]n[NaPO3(OH)]2 where n can be as great as 2000. In terms of their structures, these polymers consist of PO3− "monomers", with the chains are terminated by protonated phosphates.


      = In nature

      =
      High-polymeric inorganic polyphosphates were found in living organisms by L. Liberman in 1890. These compounds are linear polymers containing a few to several hundred residues of orthophosphate linked by energy-rich phosphoanhydride bonds.
      Previously, it was considered either as “molecular fossil” or as only a phosphorus and energy source providing the survival of microorganisms under extreme conditions. These compounds are now known to also have regulatory roles, and to occur in representatives of all kingdoms of living organisms, participating in metabolic correction and control on both genetic and enzymatic levels. Polyphosphate is directly involved in the switching-over of the genetic program characteristic of the exponential growth stage of bacteria to the program of cell survival under stationary conditions, "a life in the slow lane". They participate in many regulatory mechanisms occurring in bacteria:

      They participate in the induction of rpoS, an RNA-polymerase subunit which is responsible for the expression of a large group of genes involved in adjustments to the stationary growth phase and many stressful agents.
      They are important for cell motility, biofilms formation and virulence.
      Polyphosphates and exopolyphosphatases participate in the regulation of the levels of the stringent response factor, guanosine 5'-diphosphate 3'-diphosphate (ppGpp), a second messenger in bacterial cells.
      Polyphosphates participate in the formation of channels across the living cell membranes. The above channels formed by polyphosphate and poly-b-hydroxybutyrate with Ca2+ are involved in the transport processes in a variety of organisms.
      An important function of polyphosphate in microorganisms—prokaryotes and the lower eukaryotes—is to handle changing environmental conditions by providing phosphate and energy reserves. Polyphosphates are present in animal cells, and there are many data on its participation in the regulatory processes during development and cellular proliferation and differentiation—especially in bone tissues and brain.
      In humans polyphosphates are shown to play a key role in blood coagulation. Produced and released by platelets they activate blood coagulation factor XII which is essential for blood clot formation. Factor XII, also called Hageman factor, initiates fibrin formation and the generation of a proinflammatory mediator, bradykinin, that contributes to leakage from the blood vessels and thrombosis.
      Bacterial-derived polyphosphates impair the host immune response during infection and targeting polyphosphates with recombinant exopolyphosphatase improves sepsis survival in mice.
      Inorganic polyphosphates play a crucial role in tolerance of yeast cells to toxic heavy metal cations.


      Use as food additives


      Sodium polyphosphate (E452(i)), potassium polyphosphate (E452(ii)), sodium calcium polyphosphate (E452(iii)) and calcium polyphosphate (E452(iv)) are used as food additives (emulsifiers, humectants, sequestrants, stabilisers, and thickeners). They are not known to pose any potential health risk other than those generally attributed to other phosphate sources (including those naturally occurring in food). While concerns have been raised regarding detrimental effects on the bones and cardiovascular diseases, as well as hyperphosphatemia, these seem to be relevant only for exaggerated consumption of phosphate sources. In all, reasonable consumption (up to 40 mg phosphate per kg of body weight per day) seems to pose no health risk.


      See also


      Phosphoric acids
      Sodium trimetaphosphate
      Sodium hexametaphosphate


      References




      External links


      Pavlov E, Grimbly C, Diao CT, French RJ (September 2005). "A high-conductance mode of a poly-3-hydroxybutyrate/calcium/polyphosphate channel isolated from competent Escherichia coli cells". FEBS Lett. 579 (23): 5187–92. Bibcode:2005FEBSL.579.5187P. doi:10.1016/j.febslet.2005.08.032. PMID 16150446. S2CID 35616647.
      Kulaev I, Vagabov V, Kulakovskaya T (1999). "New aspects of inorganic polyphosphate metabolism and function". J. Biosci. Bioeng. 88 (2): 111–29. doi:10.1016/S1389-1723(99)80189-3. PMID 16232585.
      Kulaev I, Kulakovskaya T (2000). "Polyphosphate and phosphate pump". Annu. Rev. Microbiol. 54: 709–34. doi:10.1146/annurev.micro.54.1.709. PMID 11018142.

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    Polyphosphate - Wikipedia

    A polyphosphate is a salt or ester of polymeric oxyanions formed from tetrahedral PO 4 structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic (also called, ring) structures.

    Polyphosphate: a new player in the field of hemostasis - PMC

    Polyphosphate (polyP) is an inorganic polymer that has recently been shown to be secreted by activated platelets. It is a potent modulator of the blood clotting and complement systems in hemostasis, thrombosis, and inflammation.

    Polyphosphate may have utility as a hemostatic agent, whereas antagonists of polyphosphate may function as novel antithrombotic/anti-inflammatory agents. The detailed molecular mechanisms by which polyphosphate modulates blood clotting reactions remain to be elucidated.

    Are Polyphosphates Bad For You? - Here Is Your Answer.

    Dec 19, 2023 · Studies have illuminated a possible link between high polyphosphate intake and cardiovascular issues. Here's what some of the findings suggest: A 2012 study published in the Journal of Biological Chemistry found that polyphosphates can induce vascular calcification, a risk factor for heart disease, by promoting the differentiation of vascular ...

    Frontiers | Polyphosphate: A Multifunctional Metabolite in ...

    Polyphosphate (polyP), a polymer of orthophosphate (PO 4 3-) of varying lengths, has been identified in all kingdoms of life. It can serve as a source of chemical bond energy (phosphoanhydride bond) that may have been used by biological systems …

    Polyphosphate and Its Diverse Functions in Host Cells and …

    Polyphosphate (polyP) is a linear polymer of a few to many hundreds of phosphate (P i) residues linked by high-energy phosphoanhydride bonds . This ubiquitous polymer is found in bacteria, protists, and mammalian cells, and it was likely present prebiotically .

    Polyphosphate - an overview | ScienceDirect Topics

    Polyphosphate (polyP) is a highly anionic inorganic polymer composed of phosphate monomers, connected by high-energy phosphoanhydride bonds [25]. PolyP of varying lengths is ubiquitously found in every prokaryotic and eukaryotic cell.

    New Clues on Protein Fibrils Could Transform Alzheimer’s Research

    Oct 31, 2024 · A recent study reveals that a polymer called polyphosphate may stabilize fibrils, protein structures linked to Alzheimer's, Parkinson's, and other neurodegenerative diseases.

    An Update on Polyphosphate In Vivo Activities - PubMed

    Aug 2, 2024 · Polyphosphate (polyP) is an evolutionary ancient inorganic molecule widespread in biology, exerting a broad range of biological activities. The intracellular polymer serves as an energy storage pool and phosphate/calcium ion reservoir …

    Poly-P as Modulator of Hemostasis, Thrombosis, and Inflammation

    Dec 7, 2017 · Polyphosphate (polyP), consisting of linear polymers of inorganic phosphates, is ubiquitous in biology. PolyP metabolism has been most extensively explored in microbes, but until very recently, roles for polyP in mammalian cells have been poorly understood.