Page 189 - The Biochemistry of Inorganic Polyphosphates

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Algae 173
yet to come to a firm conclusion as to whether the accumulation of PolyP in algae in the
light is directly linked to photosynthesis itself, or if their formation is merely promoted by
increased ATP (and perhaps pyrophosphate) during photosynthetic phosphorylation.
Kanai and Simonis (1968) showed that, although 32 P incorporation in PolyP proceeded
more rapidly in the light and decreased in darkness, PolyP synthesis did continue to some
extent. It was concluded that PolyP synthesis in algae occured without the involvement
of photosynthesis, although it was strongly promoted by the latter process. Similar results
were obtained by Domanski-Kaden and Simonis (1972) on Ankistrodesmus braunii, and
by Overbeck (1961, 1962) on Scenedesmus quadricauda. The fact that photosynthesis is
not obligatory for PolyP accumulation was demonstrated in experiments with Euglena
(Smillie and Krotkov, 1960). Substantial amounts of PolyP were found in this organism
under heterotrophic growth (Smillie and Krotkov, 1960). Furthermore, it was shown that in
Scenedesmus obliquus PolyP was produced by glycolytic phosphorylation when this alga
was grown in the dark (Kulaev and Vagabov, 1967).
It can therefore be concluded that some part, if not all, of the PolyP formed in the algal
cells is produced independent of photosynthesis and photosynthetic phosphorylation. A
further contribution to the understanding of this problem was made by the investigations
of Miyachi and co-workers (Miyachi, 1961; Miyachi and Miyachi, 1961; Miyachi and
Tamiya, 1961; Miyachi et al., 1964) which has shown that only one of the four PolyP
fractions of Chlorella was formed in the light. This was fraction C, which was precipitated
by neutralization of a 2N KOH extract with HClO 4 in the presence of KClO 4. This fraction
waslocalized,intheopinionoftheauthors,eitherinchloroplastsorintheirvicinity(Miyachi
et al., 1964). Fraction A (extractable by 8 % trichloracetic acid) was found in volutine, and
its accumulation depended on photosynthesis only to a certain extent, probably because this
fraction was derived from fraction C through degradation. The biosynthesis and degradation
of the alkali-soluble fractions B and D (see Chapter 2) were shown to be absolutely unrelated
to photosynthesis. Their metabolism depended on the presence of P i in the medium. Similar
results were obtained with Ankistrodesmus braunii (Kanai and Simonis, 1968).
Miyach and co-workers (Miyachi, 1962; Miyachi and Miyachi, 1961; Miyachi and
Tamiya, 1961; Miyachi et al., 1964) have shown that utilization of different PolyP fractions
for nucleic acid biosynthesis in Chlorella is different in the light and in the dark. In the
opinion of these authors, PolyPs of different fractions are involved in the biosynthesis of
nucleic acids and other compounds in different ways. In the light, fraction C is a phosphorus
donor for the biosynthesis of chloroplast DNA, while fraction A is involved in the synthesis
of nuclear DNA. RNA is not formed in this alga from PolyP under conditions of P i suffi-
ciency, although PolyPs of fractions B and D are utilized for RNA biosynthesis when P i is
absent in the medium. In the light, the PolyPs of these fractions are hydrolysed to P i , which
is then utilized for the biosynthesis of RNA and other compounds. In the dark and in the
absence of P i , PolyP seems to be able to provide phosphate for RNA synthesis.
Some authors doubt the possibility of a direct interrelation between PolyP and photo-
synthesis in algae (Rubtsov et al., 1977; Rubtsov and Kulaev, 1977). The following facts
support this point of view. No high-molecular-weight PolyP was found in the chloroplasts
of Acetabularia mediterranea (Rubtsov et al., 1977). The inhibitor analysis and detection
of polyphosphate kinase activity in this alga (Rubtsov and Kulaev, 1977) point to the fact
that PolyP is not directly, but rather indirectly, connected with the photosynthesis through
the formation of ATP, which provides energy for P i transport and PolyP synthesis.