Page 168 - The Biochemistry of Inorganic Polyphosphates

WU095/Kulaev
WU095-08
Peculiarities of polyphosphate metabolism
152 March 9, 2004 20:32 Char Count= 0
2.4 b a
Glucose (mg ml −1 ) 16 OD 530 1.6 c 0.3 P (mg ml −1 )
20
2.0
12
1.2
20 8 0.8 0.2
4 0 0.4 0 3 6 10.5 15 24 0.1
µg P (g dry biomass × 10 −3 ) −1 12 8 Time (h)
16

4

0
1 2 34 56 1 2 34 56 1 2 34 56 1 2 34 56 1 2 34 56 1 2 34 56
0 3 6 10.5 15 24
Time (h)

Figure 8.17 Changes in the content of different PolyP fractions during growth of Saccharomyces
cerevisiae on glucose (Vagabov et al., 1998): (1) PolyP(I); (2) PolyP(II); (3) PolyP(III); (4) PolyP(IV);
(5) PolyP(V); (6) total PolyP content. Inset: (a) cell growth; (b) glucose concentration in the medium;
(c) P i concentration in the medium.

always significantly different and depend on the growth stage (Figure 8.18). This becomes
especially evident when comparing the changes in the degree of polymerization of the
fractions of PolyP(II), PolyP(III) and PolyP(IV). In all of these fractions, the PolyP chain
is drastically shortened during the first 3 h of yeast growth. In the case of PolyP(III) and
PolyP(IV), this shortening took 6 h of culture growth in a complete medium. The degrees
of polymerization of these fractions were found to increase again only in a 24 h culture
(Figure 8.18). These data support the assumption that in a P i -sufficient growth medium
PolyPs may act as reserves of energy, which are replenished when the carbon sources have
been depleted.
The accumulation of PolyPs (accompanied by their dramatic shortening) in actively
growing yeast cells indicates that the processes of PolyP synthesis and depolymerization
may occur in parallel. Exopolyphosphatases (Lichko et al., 2003a) and endopolyphos-
phatase (Kumble and Kornberg, 1995) could be involved in the depolymerization of PolyPs.
The active synthesis of PolyPs, accompanied by dramatic decreases in their lengths in the
logarithmic phase of S. cerevisiae growth in a carbon- and phosphorus-sufficient medium,
suggests that the energy derived from PolyP hydrolysis is necessary to maintain the high
rate of yeast growth.