Page 181 - The Biochemistry of Inorganic Polyphosphates

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Other fungi (mould and mushrooms) 165
was proposed (Vagabov, 1988). However, the ways of involving phosphatases in PolyP
metabolism in yeast are still obscure. For example, the strains of Schizosaccharomyces
pombe with mutations in the structural genes for three different phosphatases, i.e. PHO1,
PHO2 or PHO3, degraded PolyPs at the same rate as the wild-type strain during phosphate
starvation and showed the same type of over-compensation when phosphate was added
again (M¨uller et al., 1992).
To summarize, it must be said that mutational analysis and modern genetic methods
have proved to be a great success in studies of PolyP metabolism in yeast and will provide
new knowledge in this field in future. Data on the role of P i transport systems in PolyP
metabolism of yeast have been summarized in a recent review (Persson et al., 2003).
In conclusion, it should be noted that PolyP accumulation and utilization in yeast de-
pends strongly on the culture conditions and cell development stage. A great difference
has been observed in the dynamics of separate PolyP fractions and in the effects of some
culture conditions on the PolyP content in some cellular organelles. Each compartment of
the yeast cell possesses its own exopolyphosphatases (see Chapter 6) and probably its own
endopolyphosphatases and other PolyP-metabolizing enzymes. One of the intriguing ques-
tions in the study of PolyP metabolism in yeast is the pathways of its biosynthesis. Despite
many reports that have shown polyphosphate kinase activity in these organisms (Felter and
Stahl, 1973; Shabalin et al., 1979; Kornberg et al., 1999; McGrath and Quinn, 2000), this
enzyme was not purified and no gene ecoding it was found in yeast genomes (Kornberg,
1999; Zhang et al., 2002). The role of this activity in PolyP accumulation in yeast is still
obscure. The activity of other PolyP-synthesizing enzymes, such as 1,3-diphosphoglucerate
kinase and dolychil polyphosphate kinase, is not so significant for providing the synthesis
of all PolyPs in yeast cells. An assumption was made that exopolyphosphatases or en-
dopolyphosphatase may synthesize PolyP in a similar way to ATPases or pyrophosphatases
by a reverse reaction (Kulaev and Vagabov, 1983; Vagabov et al., 2000; Kulaev et al., 1999).
However, no evidence for the actual existence of such a process has been obtained. There
is no doubt, however, that PolyP synthesis in yeast is dependent on the energetic status of
the cell, in particular, on the ionic gradients on the membranes.

8.11 Other Fungi (Mould and Mushrooms)

The metabolism of PolyP has been investigated during onthogenetic development in many
fungi(Bajajetal.,1954;BelozerskyandKulaev,1957;Nishi,1961;Harold,1962a,b;Kulaev
et al., 1960a-c; 1961; 1966a, 1968; 1970a–d); Kritsky and Kulaev, 1963; James and Casida,
1964; Kulaev and Uryson, 1965; Kritsky et al., 1965a,b, 1968, l972; Mel’gunov and Kulaev,
1971; Kulaev, 1973; Okorokov et al., 1973a,b; Trilisenko et al., 1980, 1982a,b). It was
revealed that the rapid synthesis of acid-insoluble PolyPs took place during the germination
32
of fungal spores. Using P it was shown that the formation of highly polymerized PolyP at
this development stage involves utilization of less polymeric acid-soluble PolyP, resulting
in a complete conversion of the latter into an acid-insoluble form (Kulaev and Belozersky,
1962a,b). During this period of development, the endopolyphosphatase was found to be
inactive in mould fungi (Kritsky et al., 1972). This seems to facilitate to a great extent the
accumulation of large amounts of PolyPs. On the other hand, at this time PolyPs began to
be utilized for the synthesis of a variety of compounds. Nishi (1961) showed that PolyP
utilization for the synthesis of nucleotides, sugar phosphates and RNA had already started