Page 72 - The Biochemistry of Inorganic Polyphosphates

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Localization of polyphosphates in cells
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Figure 5.1 PolyP granules in Myxococcus xanthus (magnification 110 000×).

microorganisms may depend on the methods of extraction and assay. At cell fractionation,
labile PolyP may degrade. The results obtained by 31 P NMR spectroscopy also have to be
interpreted with a certain caution, considering the presence of ‘NMR-invisible’ PolyP in
some compartments (see Chapter 2). The content of PolyP varies depending on the cultiva-
tion conditions. Nevertheless, using a combination of cytochemistry, chemical extraction,
NMR spectroscopy and cell sub-fractionation methods, reliable data on PolyP localization
in eukaryotic cells have been obtained.
Intracellular localization of PolyP in eukaryotes has been most extensively studied in
yeast and fungi. Since the earliest works of Wiame (1946, 1947a,b, 1948, 1949, 1958),
it has been known that PolyPs, or at least some part of them, are present in yeast
cells as volutin granules. Such granules, containing about 14 % of the total PolyP con-
tent in yeast cells, four basic proteins and metal ions, were isolated by Jacobson et al.
(1982). The chain length of the PolyP in isolated granules was estimated to be > 3000
phosphate residues, but other methods give values of no more than 100–200 residues
for the whole yeast cell (Vagabov et al., 1998; Ogawa et al., 2000a). Volutin granules
were found in the cytosol and vacuoles by cytochemical method (Voˇr´ıˇsek et al., 1982).
The content of PolyP in the cytosol depends on culture age and cultivation conditions.
The cytosol fraction may contain 10 % (Okorokov et al., 1980) to 70 % (Trilisenko
et al., 2002) of the PolyP cell pool in cells of S. cerevisiae. In yeast, its amount in the
cytosol increases about twofold under the so-called ‘phosphate overplus’, when cells are
transferred from the medium without phosphate to a medium with phosphate (Trilisenko
et al., 2002).
The first attempts to determine the intracellular localization of PolyPs in eukaryotes
were made long ago. The earliest investigations aimed at establishing the localization of