Page 111 - The Biochemistry of Inorganic Polyphosphates

March 9, 2004
15:39
Char Count= 0
WU095/Kulaev
WU095-07
Energy source 95
3−
PO 4 + H +
+
PolyP ∆µH use
ATP P i

+
∆µH generation
ADP

MeHPO 4

Figure 7.1 The interrelations between ATP and PolyP in bacteria ( µH is the electrochemical H +
+
potential).

latter energy recycling mechanism by providing the efflux process with a continuous supply
of P i (Kortstee et al., 2000). The known interrelations between ATP and PolyP metabolism
in bacteria are shown in Figure 7.1.

7.2.2 Polyphosphate in Bioenergetics of Eukaryotes

In eukaryotes, little direct evidence of the interrelation between the AMP–ADP–ATP system
and PolyPs has been found. Polyphosphate kinase genes are absent in the known eukaryotic
genomes (Kornberg et al., 1999; Zhang et al., 2002). NAD kinases and glucokinase of
eukaryotes have lost the ability to use PolyP as a phosphodonor. It seems that the role
of PolyP in bioenergetics is diminished in eukaryotic cells. However, some data suggest
preservation of the PolyP function as an energy reserve in eukaryotic microorganisms.
First, the synthesis of ATP from PolyP has been observed in isolated vacuoles of yeast
(Schabalinetal.,1977).However,thesignificanceofthisprocessneedsfurtherinvestigation.
Secondly, the induction of high-molecular-weight PolyP synthesis in yeast cells took
place in parallel with the exit of K + ions from the cells under accumulation of diva-
lent cations in the presence of glucose (Okorokov et al., 1983a,b). This accumulation
(Figure 7.2) was not affected by antymicine A but completely prevented by ionophores,
+
stimulating K /H exchange and disturbance of the K gradient on the plasma membrane.
+
+
ThissuggestsapossibilityofPolyPparticipationinretentionoftheenergyoftransmembrane
K gradient. PolyP accumulation in the yeast cell under phosphate overplus conditions was
+
inhibited by 50 % by the protonophoric uncoupler FCCP (Trilisenko et al., 2003). This sug-
gests involvement of the energy of proton motive force in PolyP synthesis. At the same time,
it was observed that PolyP hydrolysis in S. cerevisiae was induced by the protonophoric
uncoupler CCCP (Beauvoit et al., 1991).
Thirdly, observations of the PolyP dynamics during the growth of S. cerevisiae give
additional indirect evidence of PolyP participation in the processes of energy conservation in