Page 105 - The Biochemistry of Inorganic Polyphosphates

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Enzymes of polyphosphate degradation 89
kinase, ppk2, discovered in Pseudomonas aeruginosa in compliance with its substrate
specificity and predominant reaction pathway (Ishige et al., 2002, Zhang et al., 2002).
Thus, in E. coli and P. aeruginosa the PolyP:AMP phosphotransferase activity is a
result of the joint action of adenylate kinase and polyphosphate kinases. The occurrence of
PolyP:AMPphosphotransferase in the above bacteria has, however, no genetic confirmation.
No such activity was observed in eucaryotes, in line with the absence of polyphosphate
kinase.
The analysis of the properties of PolyP-dependent enzymes has offered some inter-
esting observations. The sets of PolyP-dependent enzymes in procaryotes and eucaryotes
show a significant difference. Some enzymes are found in only procaryotes or in eucary-
otes (Table 6.8). Even the exopolyphosphatases of procaryotes and eucaryotes belong to
different protein families. Tight interrelations between PolyPs and the enzymes metabo-
lizing nucleoside compounds are most demonstrated in procaryotes (Figure 6.7), whereas
in eucaryotes these interrelations are weaker. Nevertheless, some reactions linking PolyPs
and nucleoside–polyphosphate pools are also observed (Booth and Guidotti, 1995; Ku-
lakovskaya et al., 1997; Guranowski et al., 1998).
It should be noted that many PolyP-dependent enzymes (polyphosphate kinase, ex-
opolyphosphatases, PolyP glucokinase and NAD kinase) are multifunctional and can catal-
yse reactions both with PolyPs and nucleotide triphosphates. Some PolyP-dependent en-
zymes, especially exopolyphosphatases, provide excellent examples of cell-compartment
specific enzymes. Cell-compartment specificity is a characteristic feature of eucaryotic
ATPases (Nelson, 1992) and pyrophosphatases (Baltscheffsky and Baltscheffsky, 1992;
Davies et al., 1997; Baykov et al., 1999). This means that the same reaction may be per-
formed in cell compartments by specific enzymes, which differ in their properties, encoding
genes and functions. All of the above properties of PolyP-dependent enzymes suggest their
important role in the regulation of living cell functions as a whole.