Page 134 - The Biochemistry of Inorganic Polyphosphates

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Functions of polyphosphate and polyphosphate-dependent enzymes
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for the fungus Aspergillus niger (Kulaev and Belozersky, 1958; Mudd et al., 1958; Stahl
et al., 1964). It was shown that PolyPs are utilized primarily for the biosynthesis of RNA
in Penicillium chrysogenum (Kulaev et al., 1959; Kritsky et al., 1968) Lenthius tigrinus
(Kritsky and Belozerskaya, 1968; Kritsky et al., 1968). A clear correlation between the
content of salt-soluble PolyPs and that of RNA was observed. The participation of PolyPs
in nucleic acid metabolism was proposed to be connected with the consumption of the
activated phosphorus of the PolyP for nucleic acid biosynthesis (Kulaev, 1979; Kulaev and
Vagabov, 1983). In discussing the interaction of PolyP metabolism with that of nucleic
acids in eukaryotic cells, it is pertinent to mention that PolyPs may also form complexes
with RNA (Kulaev and Belozersky, 1958). PolyP 60 was found in DNA preparations from
filamentous fungal species of Colleotrichum (Rodriguez, 1993).
The polyP content and polymerization degree have a intricate dynamic during culture
growth in yeast and fungi (see details in Chapter 8). This dynamic correlates with the growth
stage and indicates the interrelation of PolyP metabolism and culture development. In yeast,
the double mutation in exopolyphosphatase PPX1 and endopolyphosphatase genes results
in a diminished ability to survive in the stationary-growth phase (Sethuraman et al., 2001).
The above genes was concluded to be essential for stationary-phase adaptation in yeast
(Sethuraman et al., 2001).
One of the developmental processes in lower erucaryotes is antibiotic synthesis. Some of
the data obtained indicated the interaction between PolyP metabolism and the above process
(Kulaev and Vagabov, 1983). It was shown that the levels of PolyP (fractions PP1, PP2 and
PP3) in the strain of Penicillium chrysogenum intensively producing penicillin were two to
three times higher than those in the low-productive strain during the period of penicillin
production (Telesnina et al., 1985). In contrast, strains of Tolypocladium sp. differing in
cyclosporine production levels were similar in their PolyP contents (Sotnikova et al., 1990).
The level of PolyP was lowered two- to threefold during the period of intensive growth and
at the beginning of antibiotic synthesis (Sotnikova et al., 1990). In Fusidium coccineum,
the PolyP level was lower in the high-fusidic-acid-producing strain than that in the strain
with a low production of the antibiotic (Navashin et al., 1983). These authors proposed that
PolyP was used as an energy source for antibiotic biosynthesis. Thus, while the mechanisms
of the interactions of PolyP metabolism and antibiotics biosynthesis in eukaryotes are still
unknown, the interactions between both processes probably depend on the microorganism
species, culture conditions and P i content in the medium.
To summarize, in lower eukaryotes the participation of PolyPs in development processes,
gene activity control and overcoming stress is confirmed at present by much indirect ev-
idence and thus establishment of the background for such functions is one of the major
future tasks in PolyP biochemistry.

7.8 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.