Polyphosphate

Polyphosphates are anionic phosphate polymers linked between hydroxyl groups and hydrogen atoms. The polymerization that takes place is known as a condensation reaction. Phosphate chemical bonds are typically high-energy covalent bonds, which means that energy is available upon breaking such bonds in spontaneous or enzyme catalyzed reactions. Adenosine triphosphate (ATP) is an example of a phosphate trimer, a polymer with three phosphate groups. In many species they are stored in acidocalcisome‎s.

Examples of Polyphosphates

Sodium Triphosphate

Sodium triphosphate, (Na₅P₃O₁₀), has been used widely as a constituent of laundry detergents, acting as a water softener in hard water regions and improving detergent performance. In recent years, concern has grown that this results in substantial amounts of phosphates entering the sewage system and thence to watercourses, resulting in eutrophication. This has led to the amounts of polyphosphates in detergents being legally controlled in a number of countries (e.g., Germany, Italy, Austria).

Sodium triphosphate is, beside potassium triphosphate, one of the triphosphate compounds that are allowed as food additive and is known as E451.

High-polymeric Inorganic Polyphosphates

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 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 line”. 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 Factor XII which is essential for blood clot formation. Furthermore platelets-derived polyphosphates activate blood coagulation factor XII (Hageman factor) that initiates fibrin formation and the generation of a proinflammatory mediator, bradykinin that contributes to leakage from the blood vessels and thrombosis..

External links

• Kulaev I, Vagabov V, Kulakovskaya T (1999). "New aspects of inorganic polyphosphate metabolism and function". J. Biosci. Bioeng. 88 (2): 111–29. PMID 16232585. CS1 maint: Multiple names: authors list (link)
• 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. 

References

ca:Polifosfat uk:Поліфосфат