Page 164 - The Biochemistry of Inorganic Polyphosphates

WU095/Kulaev
WU095-08
Peculiarities of polyphosphate metabolism
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Thesynthesisanddegradationofthesefractionsarecloselyrelatedtometabolicprocesses
inindividualcellcompartments,andtheirdynamicsareaffectedindifferentwaysbychanges
in the culture conditions.

8.10.2 The Dynamics of PolyP Fractions during
the Cell Cycle
The relationship between the metabolism of various PolyP fractions, RNA and DNA in syn-
chronous cultures of the yeast Schizosaccharomyces pombe (synchronicity index, 0.7–0.8)
has been investigated (Kulaev et al., 1973b). As shown in Figure 8.14, there were sub-
stantial changes in the amounts of a wide variety of phosphorus compounds in the interval
between the two episodes of division, i.e. during the growth of dividing cells. The shape
of the curve for total phosphorus accumulation during this period is mainly determined
by accumulation of RNA in the cells. The amount of DNA is doubled over a short time
interval (∼ 15 min) and reaches its maximum at the beginning of the next episode of cell
division. During the first two thirds of the period of synchronous growth of S. pombe, the
total PolyP content increased. In the period immediately preceding cell division, a slight
fall in PolyP accumulation was observed. Fractions PolyP(III) and PolyP(IV) accumulated
rapidly at the beginning of this period. Accumulation of PolyP(IV) appeared first. These
data are in agreement with the opinion that these fractions are synthesized in connection
with the biosyntheses of the cell wall polysaccharides mannan and glucan (Kulaev et al.,
1972d). Fraction PolyP(II) accumulated in the cells of the synchronous culture in corre-
lation with the RNA biosynthesis. It is probable that the formation of PolyP(II) and the
nucleic acids biosynthesis are linked as shown in Figure 8.15. Using the 32 P isotope, it
was shown that the phosphorus of the PolyP might incorporate with RNA synthesis to the
same extent for all of the nucleosides (Kulaev and Belozersky, 1957). As regards PolyP(I),
its behaviour is converse to that of the total RNA. This fraction is apparently a reserve
of high-energy phosphate and is probably used during the intensive synthesis of nucleic
acids. On the basis of these results, the following outline of the PolyP relationship during
the cell cycle in the yeast S. pombe may be proposed. During the biosynthesis of RNA,
the high-energy phosphate of PolyP(I) is utilized. On the other hand, the PP i formed in the
nucleus during the RNA (DNA) biosynthesis may be a source for the synthesis of PolyP(II).
By depolymerization of these fractions, restoration of the PolyP(I) fraction may occur. The
PolyP(III) and PolyP(IV) fractions are apparently connected with the formation of the cell
wall during cell division and are not involved in nucleic acid biosynthesis. Thus, the data
obtained on the synchronous culture of yeast gave evidence of the different roles of PolyP
fractions during the cell cycle.
In the S. cerevisiae synchronous culture, an increased P i uptake from the culture medium
during DNA synthesis was observed (Gillies et al., 1981). At a high level of external P i , this
uptake provided the necessary phosphorus level in cells and the 31 P ‘NMR-visible’ PolyP
remained constant. However, if the external P i content was low, this PolyP was consumed,
acting as a substitute for the phosphate reserve (Gillies et al., 1981).
A complicated and indirect interaction of the mitosis specific activation of the P i -
responsive gene PHO5 and the PolyP level in S. cerevisiae has been found (Neef and
Kladde, 2003). PHO5 mitotis activation was repressed by P i addition, which significantly