The Functions of Polyphosphates in Higher Eukaryotes

The cells of higher eukaryotes posesses PolyPs but in smaller amounts than those found in microorganisms. The main function of these biopolymers is probably their participation in regulatory processes. 

Few data are available on the PolyP function in higher plants. PolyPs were first observed in maize roots (Vagabov and Kulaev, 1964), while Niemeyer studied PolyPs and their interactions with the inositol phosphate pools in plants (Niemeyer, 1975, 1976, 1999 Niemeyer and Selle, 1989). Some data on the dynamics of PolyPs during the development of cotton plants were obtained (Valikhanov et al., 1980). It is probable that some plants can use extracellular PolyP as a phosphorus source (Igamnazarov and Valikhanov, 1980). 

As for animals, PolyPs were first found in their cells by Gabel and Thomas (1972). The role of PolyPs in animal cells is still little studied, but some important facts indicate their importance in development and regulatory processes. 

The activity of endopolyphosphatase was also found in animal brain. An endopolyphos-phatase had been partially purified from rat and bovine brain, where its abundance was about 10 times higher than that in their other tissues but less than a tenth of that in yeast the end product of digestion of a partially purified brain enzyme is tripolyphosphate (Kumble and Kornberg, 1996). 

One example of the probable regulatory function of PolyPs in animals is the ability of these polymers when added to culture media to enhance the proliferation of normal human fibroblast cells. PolyPs also enhanced the mitogenic activities of acidic fibroblast growth factor (FGF-1) and basic fibroblast growth factor (FGF-2). A physical interaction between PolyP and FGF-2 was observed, which stabilized this protein. Furthermore, PolyPs facilitated the FGF-2 binding to its cell surface receptors (Shiba et al, 2003). 

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