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VOL. 72 (3), 463-487, 2006 SPECTROPHOTOMETRIC CHARACTERISATION OF THE...

iii) the biosynthesis of proteins: certain transferases such as
glutamine synthetase adenylyltransferase (EC 2.7.7.42),
which participates in the regulation of glutamine synthetase
(EC 6.3.1.2), transfer one monophosphate nucleotide from a
triphosphate nucleotide, with the release of PPi; the enzymes
called aminoacyl-tRNA synthetases catalyse the binding of
each aminoacid with the corresponding tRNA, with the
concomitant release of PPi from ATP;

iv) the recovery of nitrogenous bases: hypoxanthine
phosphoribosyltransferase (EC 2.4.2.8) catalyses the transfer
of a residue of ribose-5-phosphate from phosphoribosyl-PPi
to a purine such as hypoxanthine or guanine, releasing a
nucleotide and PPi; other enzymes of this group work in the
same way to recover other bases.

In all the examples cited, further hydrolysis of PPi by
pyrophosphatase (EC 3.6.1.1) drives the equilibria in these reactions
towards the corresponding anabolic sense.

The quantification of PPi is important not only to assess its
presence and concentration in a sample, but also to determine
enzymatic activities. Thus, the measurement of PPi released by a
DNA polymerase can be used to quantify viral charge (3) or to
determine the presence of PPi in animal (4) or plant (5) tissues. PPi
is usually excreted in urine, and the PPi concentration is usually
monitored as an indicator of renal function (6). Accordingly, the
measurement of increased of PPi excretion in urine is the basis for
confirmation of the diagnosis of the rare inherited disorder
hypophosphatasia (7). Furthermore, in the industry PPi is often used
as a additive in dentifrices, making it necessary to develop processes
able to assess its concentration (8).

Several methods have been developed for the determination of
PPi. The classical chemical method quantifies total phosphates by
the generation of ammonium phosphomolybdate (9). Other
approaches resolve the components of a sample by chromatography
(10) or capillary electrophoresis (11) and quantify the corresponding
compounds. Finally, the PPi-mediated quenching of fura-2
fluorescence can also be used to determining phosphate polymers of
different lengths (12). In the biochemistry laboratory, PPi is

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