Purines are biochemically significant as components of DNA and RNA, and are also found in a number of other important biomolecules, such as ATP, GTP, cyclic AMP, NADH, and coenzyme A.
Purines are biologically synthesised as nucleosides (bases attached to ribose).
Purines from food (or from tissue turnover) are metabolised by several enzymes, including xanthine oxidase, into uric acid.
Purine and pyrimidine ribo- and deoxyribonucleotides may be synthesised de novo from simple molecules by energetically expensive, multistep pathways.
It is equally noteworthy that for both purine and pyrimidine metabolism, direct interconversions of the aminated nucleosides (adenosine, cytidine) with the corresponding bases (adenine, cytosine), or deamination at the base level, occur only in microorganisms and not in man. These differences are important for the design of effective antibiotic therapy.
For instance, a considerable amount of adenosine is produced endogenously (14-23 mmol/24 h in adults) as a by-product of the S-adenosylmethionine methylation pathway, a fraction of this being compartmentalised by protein binding.
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