Page 170 - The Biochemistry of Inorganic Polyphosphates

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Peculiarities of polyphosphate metabolism
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Figure 8.19 The PolyP content (a) and cell growth (b) of Saccharomyces cerevisiae under different
culture conditions (Vagabov et al., 2000): (1) PolyP(I); (2) PolyP(II); (3) PolyP(III); (4) PolyP(IV);
(5) PolyP(V); (6) total PolyP content. The points indicate the following: (A) re-inoculation from
complete medium to the medium without P i ; (B) re-inoculation to the complete medium after growth
on the medium without P i ; (C) and (D) growth in the complete medium for 2 and 4 h, respectively
(after re-inoculation from the medium without P i ).

its fixed content suggests that yeast cells possess an unknown discrete pathway of PolyP
biosynthesis, which results in the formation of comparatively low-molecular-weight chains
and then of high-molecular-weight polymers (Figure 8.20). The different behaviours of
the separate PolyP fractions during phosphate overplus suggests that the mechanism of
the synthesis of distinct PolyP fractions may be different or at least regulated in different
ways.
The phosphate overplus phenomenon is achieved in S. cerevisiae not only after the
complete absence of P i in the culture medium, but also after P i limitation (Kulakovskaya
et al., 2004) (Figure 8.21). The dynamics of changes in the PolyP content of separate frac-
tions was studied at re-inoculation of late-logarithmic cells from P i -limited to complete
medium. The PolyP(I), PolyP(II) and PolyP(III) fractions increased more significantly dur-
ing the first 2 h of cultivation. After further cultivation, some redistribution of PolyPs be-
tween the fractions took place. The content of the PolyP(I) fraction decreased while those of
the PolyP(II), PolyP(III) and PolyP(V) fractions increased in the stationary phase, although
the content of PolyP(IV) changed insignificantly (Figure 8.21). Its twofold increase in the
stationary phase was mainly due to the PolyP(III) and PolyP(V) fractions (Figure 8.21).