Page 212 - The Biochemistry of Inorganic Polyphosphates

WU095/Kulaev
WU095-10
Polyphosphates in chemical and biological evolution
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hexose sugar phosphates, which may be considered as a model for precursor components
of RNA (Arrhenius et al., 1993; Pitsch et al., 1995; De Graaf et al., 1998). Other minerals,
e.g. montmorillonites, catalyse self-condensation of 5 -phosphorimidazolide of nucleosides

in pH 8 aqueous electrolyte solutions at ambient temperatures leading to the formation of
RNA oligomers (Ferris and Ertem, 1993; Ertem and Ferris, 1997, 1998). These model
experiments support the postulate that the origin of the ‘RNA world’ was initiated by
RNA oligomers produced by polymerization of activated monomers formed in the course
of prebiotic processes (Ferris and Ertem, 1993; Ertem and Ferris, 1997, 1998). It is not
improbable that P i , oligophosphates and PolyP as active anions might have possibilities for
modulating the adsorbtion and catalytic properties of the above minerals and thereby affect
the synthetic processes at the earliest stages of chemical evolution.
Phosphate minerals might have taken an important place at the earlier stages of chemical
evolution and in the model experiments reconstituting the biomolecular stage of evolution

on the Earth. For example, non-enzymatic formation of 5 -ADP, starting from phosphory-

lation of 5 -AMP in the presence of either calcium phosphate or calcium pyrophosphate
precipitates, has been reported. This reaction was taken as a model example for the study
of heterogeneous catalysis of transphosphorylation in prebiotic conditions (Tessis et al.,
1995). Depending on the precipitation times of the samples and medium composition, the
structural analysis of these precipitates by electron and X-ray diffraction showed changes
in their ‘grade’ of crystallinity. It was proposed that these changes are responsible for mod-
ulation of the quantity of adsorbed nucleotides to the surface of solid matrices, as well as
the catalytic activity of the precipitates (Tessis et al., 1995).
Many model experiments (Fox and Harada, 1958, 1960; Ponnamperuma et al., 1963;
Schramm et al., 1962, 1967; Rabinowitz et al., 1968; Schwartz and Ponnamperuma, 1968;
Gabel and Ponnamperuma, 1972; Schoffstall, 1976; Oro, 1983) have shown that high-
molecular-weight PolyPs, in contrast to pyrophosphate, could have functioned on the
primeval Earth as condensing agents in reactions leading to the formation of nucleosides, nu-
cleotides(includingadenosinetriphosphate),simplepolynucleotides,polypeptidesandeven
primitive protein-like materials. It should be noted that divalent cations, especially Mg ,
2+
were often needed for effective realization of these processes. For example, condensation
of glycylglycine to oligoglycine with cyclotriphosphate in an aqueous solution containing
Mg 2+ have been observed (Yamagata and Inomata, 1997). Magnesium ion was found to
have a remarkable catalytic effect on the phosphorylation of adenosine by cyclotriphos-
phate in an aqueous solution under mild conditions at pH 7.0 and 41 C. The product was
◦

primarily 2 ,3 -cyclic AMP, together with lesser amounts of ATP (Yamagata et al., 1995).

Some observations proposed that PolyP may be a catalyst in the abiotic synthesis of
peptides (Rabinowitz et al., 1969; Rabinowitz and Hampai, 1984; Chetkauskaite et al.,
1988).
It was observed that condensation reactions, in which high-molecular-weight PolyPs
functioned as activating agents, could be carried out either at high temperatures in non-
aqueous media or at room temperature in an aqueous solution. This gives grounds to suppose
that these reactions could be involved in the synthesis of macromolecules, which were
subsequently incorporated into living cells, both before and after the appearance of the
hydrosphere on Earth (Kulaev, 1971, 1973).
Prebiological energy conversion at the prenucleotide level was suggested to involve
a ‘thioester world’ (De Duve, 1987), an ‘iron–sulfur world’, in which pyrite (FeS 2 )is