Here are some more excerpts describing how our bodies process nucleoproteins
(purines and pyramidines).  It is certain that purines are critically
important to our health.  The debate is whether (1) we benefit from dietary
purines; or (2) we manufacture all the purines we need, and dietary purines
are merely a burden to be eliminated.  I doubt there is a simple answer to
this problem; most likely, individual differences must be taken into
account.

Cheers,
-- Aaron Wieland

http://www.auhs.edu/netbiochem/pupyr/pp.htm:

<<One of the important specialized pathways of a number of amino acids is
the
synthesis of purine and pyrimidine nucleotides. These nucleotides are
important for a number of reasons. Most of them, not just ATP, are the
sources of energy that drive most of our reactions. ATP is the most commonly
used source but GTP is used in protein synthesis as well as a few other
reactions. UTP is the source of energy for activating glucose and galactose.
CTP is an energy source in lipid metabolism. AMP is part of the structure of
some of the coenzymes like NAD and Coenzyme A. And, of course, the
nucleotides are part of nucleic acids. Neither the bases nor the nucleotides
are required dietary components. [for another perspective on this, see
below]  We can both synthesize them de novo and salvage and reuse those we
already have.>>

<<Purine and pyrimidine bases which are not degraded are recycled - i.e.
reincorporated into nucleotides. This recycling, however, is not sufficient
to meet total body requirements and so some de novo synthesis is essential.
There are definite tissue differences in the ability to carry out de novo
synthesis. De novo synthesis of purines is most active in liver. Non-hepatic
tissues generally have limited or even no de novo synthesis. Pyrimidine
synthesis occurs in a variety of tissues. For purines, especially,
non-hepatic tissues rely heavily on preformed bases - those salvaged from
their own intracellular turnover supplemented by bases synthesized in the
liver and delivered to tissues via the blood.>>

<<Purine de novo synthesis is a complex, energy-expensive pathway. It should
be, and is, carefully controlled.>>

http://www.auhs.edu/netbiochem/pupyr/another.htm:

<<Further, the statement that "little dietary purine is used and that which
is absorbed is largely catabolized," leaves a question of what use is the
little that isn't catabolized ? Also, purines and pyrimidines from tissue
turnover which are not salvaged are catabolized and excreted and the fact
that de novo synthesis is rather energy intensive could suggest that dietary
sources, when available, would be welcome additions to metabolism
mechanisms.>>