Page 192 - The Biochemistry of Inorganic Polyphosphates

WU095/Kulaev
WU095-08
Peculiarities of polyphosphate metabolism
176 March 9, 2004 20:32 Char Count= 0
phosphate-free medium (Blum, 1989). The short-chain PolyP content did not differ be-
tween the cells incubated for1hinthe absence of exogenous substrate or in the presence of
glucose or glycerol. The long-chain PolyP content, however, was lower in cells incubated
without glucose than in cells incubated with glucose and was also lower in cells incubated
for 1 h with glycerol, as compared with freshly washed cells. The P i and PP i increase (up to
61 %) which occurred in promastigotes incubated in the absence of an exogenous substrate
could have arisen from the concomitant decrease in the long-chain PolyP content (Blum,
1989).
Leishmania major promastigotes contain electron-dense vacuoles (LeFurgey et al.,
1990). The elemental compositions of these vacuoles and the cytoplasm were determined by
electron probe X-ray microanalysis. The electron-dense vacuoles are rich in P, presumably
present as PolyP, while Mg 2+ was about nine times higher than its cytoplasmic level and its
content was enough to neutralize most of the negative charge of PolyP. The electron-dense
2+
vacuoles also contain appreciable amounts of Ca 2+ and Zn , which are not detectable in
−
+
+
the cytoplasm, as well as Na ,K and Cl (the latter two in concentrations below that in
the cytoplasm). These results suggest that the vacuolar membranes have at least one cation
transport system. Incubation of the promastigotes for 1 h in the absence of phosphate, in-
dependent of the presence or absence of glucose, did not cause any significant changes in
the vacuolar contents of phosphorus, magnesium or zinc (LeFurgey et al., 1990).
The interaction of Entamoeba histolytica with collagen induces the intracellular for-
mation and the release of electron-dense granules containing collagenase activity, which
is important for pathogenicity of this parasite. Purified granules are a complex of mainly
cationic proteins, which contains numerous proteolytic activities, actin, and small molecules
such as P i ,PP i and cations (Leon et al., 1997). It is not improbable that such granules also
contain some quantities of PolyP.
An unusual characteristic of some protozoa is the presence in their cells of a specific
organelle, named as acidocalcisome (Docampo and Moreno, 2001). Acidocalcisome is an
electron-dense acidic organelle, which contains a matrix of pyrophosphate and PolyP with
bound calcium and other cations. Its membrane possesses a number of pumps and exchang-
ers for the uptake and release of these components. Acidocalcisome is possibly involved in
PolyP and cation storage and in the adaptation of these microoganisms to environmental
stress (Docampo and Moreno, 2001). A 31 P NMR spectroscopic study revealed the high
levels of PP i , PolyP 3 and PolyP 5 in perchloric-acid extracts of Trypanosoma brucei, Try-
panosoma cruzi and Leishmania major (Moreno et al., 2000). The 31 P NMR spectra of
purified acidocalisomes of these organisms indicated the presence of PolyP with an average
chain length of 3–4 (Moreno et al., 2000).
In Trypanosoma cruzi, the PolyP was represented by a millimolar level of PolyP with
a chain length of ∼ 50 residues and a micromolar level of longer PolyPs with a chain
length of about 700–800 residues (Ruiz et al., 2001a). The PolyP was mostly localized
in acidocalcisomes. The level of PolyP was measured at different development stages of
Trypanosoma cruzi (Ruiz et al., 2001a). A rapid increase in the PolyP level was observed
at differentiation of trypomastigote to amastigote and in the lag phase of epimastigotes
growth. Both the short- and long-chain PolyPs content increased during these development
stages. The PolyP content rapidly decreased after the epimastigotes-resumed growth.
Similar to Trypanosoma cruzi, the acidocalcisomes of Toxoplasma gondii contained
PolyPs with an average chain length ∼ 50 residues at the millimolar level and a micromolar