Page 215 - The Biochemistry of Inorganic Polyphosphates

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Polyphosphates and pyrophosphates 199

Figure10.2 SynthesisofpyrophosphateandATPinratlivermitochondria(Mansurovaetal.,1973b).

mitochondria, pyrophosphate was synthesized at about one tenth the rate of the synthesis
of ATP and ADP (AMP was present in the incubation medium). The inhibitors of the
respiratory chain, rotenone (2 µg per mg of protein), antimycin (1 µg per mg of protein),
and cyanide (1mM), together with the uncoupler 2,4-DNP (0.4 mM), completely suppressed
the biosynthesis of pyrophosphate in rat liver mitochondria. This was shown both in intact
mitochondria and in fragments of the internal mitochondrial membrane. It is possible that
pyrophosphate is formed in the mitochondria as a secondary product, by the cleavage of
some part of ATP to AMP and pyrophosphate. However, experiments on the effect of
oligomycin (2 µg per mg of protein), which inhibits the formation of ATP in mitochondria,
showed that under these conditions the production of pyrophosphate increased substantially.
These findings suggest that pyrophosphate is synthesized in animal mitochondria during the
functioning of the respiratory chain independent of ATP, and to a certain extent in opposition
to it. Similar results were obtained with yeast mitochondria (Mansurova et al., 1975b).
The lack of dependence of pyrophosphate synthesis in animal and yeast mitochon-
dria on ATP was even more established in experiments with mitochondria, which had
been depleted in ADP and ATP by pre-incubation with glucose (40 mM), hexokinase
−1
(0.1 mg ml ) and oligomycin (1 µg per mg of protein). In these experiments, the synthesis
of pyrophosphate in yeast mitochondria proceeds in the total absence of ADP and ATP
(Figure 10.3). The addition of P i enhanced the above synthesis. Much more pyrophosphate
than ATP is synthesized in the chromatophores of Rh. rubrum, whereas substantially more
ATP is formed in animal mitochondria. In addition, the quantity of pyrophosphate synthe-
sized in yeast mitochondria may approximate to their ATP content under certain conditions
of incubation.
Comparative biochemistry thus suggests that, since ancient times, and perhaps since
the appearance of the earliest organisms, pyrophosphate has been involved in energetic