Page 107 - The Biochemistry of Inorganic Polyphosphates

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THE FUNCTIONS OF

POLYPHOSPHATES AND

POLYPHOSPHATE-

DEPENDENT ENZYMES

7.1 Phosphate Reserve

Many authors have adhered to the view that PolyPs are primarily a reserve of phosphate, on
which the cells of microorganisms are able to draw on at any time, but especially during the
periods of phosphorus starvation (Mudd et al., 1958; Harold, 1966; Kulaev and Vagabov,
1983; Wood and Clark, 1988; Kornberg, 1995). This function of PolyPs is confirmed by a
strong dependence of PolyP content in the cells of microorganisms on the phosphate content
in the medium (see Chapter 8).
In the opinion of Harold (1966), PolyPs, being polymers, constitute highly convenient
compounds for the storage of large amounts of P i in the cell, since the accumulation of poly-
meric phosphate molecules has little effect on osmotic pressure within the cells and, on the
other hand, serves to maintain a constant level of important metabolites such as free P i and
ATP. Since phosphorus is an element of vital importance, which organisms are absolutely
uncapable to live without, in the course of evolution microorganisms have developed the
ability to store surplus phosphate in the form of PolyPs. It has been shown more than once
that many microorganisms, both prokaryotes and eukaryotes, may occasionally accumulate
sufficient amounts of PolyPs, thus enabling them to grow on a phosphorus-free medium
(Langen and Liss, 1958a,b; Liss and Langen, 1962; Harold, 1966; Kulaev and Vagabov,
1983).
PolyPs are the principal regulators of the intracellular level of P i in microorganisms.
In all cases of rapid P i uptake by cells, when the pathways of its utilization are limited,
PolyPs are accumulated and the intracellular concentration of P i remains low (Harold, 1966;

The Biochemistry of Inorganic Polyphosphates I. S. Kulaev, V. M. Vagabov and T. V. Kulakovskaya
C 2004 John Wiley & Sons, Ltd ISBN: 0-470-85810-9

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