Page 121 - The Biochemistry of Inorganic Polyphosphates

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March 9, 2004
15:39
WU095-07
WU095/Kulaev
Cell-envelope formation and function 105
The PolyP in the cell envelope is of great importance for maintenance of the negative
charge on the cell surfaces of fungi (Vagabov et al., 1990a; Ivanov et al., 1996). The cell-
envelope PolyPs can bind with a monovalent cation dye, 9-aminoacridine (9AA), in the
presence of an inhibitor of translocation of the dye across the plasma membrane, namely
thiamine (Theuvenet et al., 1983). From the results of measuring the absorption rate of
9AA, one can determine variations in the PolyP content in the cell envelope. Using various
P i concentrations in the medium, it is possible to initiate significant variations in the PolyP
content in yeast and to observe their effects on 9AA absorption by the cell envelope.
Phosphate starvation of cells resulted in a significant decline of their ability to absorb
9AA, while their subsequent growth on a phosphate-rich medium promoted an increase in
absorption of the dye. Interestingly, in this case the pre-treatment of cells with UO 2+ caused
a decrease in 9AA sorption of almost 80 %. These results are evidence of an appreciable
contribution of PolyP to the total negative charge of the cell envelope (Vagabov et al., 1990).
The PolyP content in cell envelopes affects the extent of cytoplasmic membrane damage
induced by different ionic compounds, in particular, a cationic surfactant – cetyltrimethy-
lammonium bromide (CTAB). It was observed that the higher the PolyP content of the cell
envelope, then the more CTAB is concentrated there, thus resulting in an intensification of
its damaging effect on the cell (Ivanov et al., 1996).
The putative pathway of coordination of mannan and PolyP biosynthesis by cell-wall
formation has been proposed (Kulaev, 1994), which explains the presence of PolyP outside
of the cytoplasmic membrane (Figure 7.4). Dolichyl–phosphates (Dol–Ps) act as transmem-
brane carriers of carbohydrate residues in glycoprotein biosynthesis. GDP–mannose at the

Figure 7.4 The putative pathway of coordination of mannan and PolyP biosynthesis in yeast.