Page 61 - The Biochemistry of Inorganic Polyphosphates

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THE FORMS IN WHICH

POLYPHOSPHATES ARE

PRESENT IN CELLS

As mentioned in Chapter 2, PolyPs may be present in living cells both in the free and
bound states. Modern methods, including 31 P NMR spectroscopy, give some evidence for
this concept. Since the classical work of MacFarlane (1936), it has been considered that
acid-soluble low-molecular-mass PolyPs are present in cells in the free state. However, the
question as to the state of the more polymeric PolyPs within a cell cannot yet be considered
as having been finally resolved.

4.1 Polyphosphate–Cation Complexes

Being polyanions, PolyPs can form complexes with different cations including biologi-
cally important Ca 2+ and Mg 2+ (Van Wazer and Campanella, 1950; Van Wazer, 1958;
Corbridge, 1980; Bonting et al., 1993a; Cini et al., 2000). The dissociation constants for
2+
2+
Mg – and Ca –polyphosphate complexes were 9.3 × 10 −2 M and 1.5 × 10 −2 M, respec-
tively (Bonting et al., 1993a).
Using electron microscopy and energy disperse X-ray microanalysis, it was shown that
2+
2+
PolyP granules of cyanobacteria contain Mg ,Ca ,Mn 2+ and other cations (Baxter
and Jensen, 1980a,b; Jensen et al., 1982). Large PolyP granules of Acinetobacter contain
2+
Mg ,Ca 2+ and K in a ratio which depends on the extracellular concentrations of the
+
above cations (Bonting et al., 1993a). In bacteria, PolyP complexes with heavy metals were
observed: with Sr 2+ and Ba 2+ in Plectonema boryanum (Baxter and Jensen, 1980 a,b), with
Ni 2+ in Staphylococcus aureus (Gonzales and Jensen, 1998), and with Cd 2+ in Anacystis
nidulans (Keyhani et al., 1996) and Escherichia coli (Keasling and Hupf, 1996; Keasling,
1997; Keasling et al., 2000).

The Biochemistry of Inorganic Polyphosphates I. S. Kulaev, V. M. Vagabov and T. V. Kulakovskaya
C 2004 John Wiley & Sons, Ltd ISBN: 0-470-85810-9

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