Purine metabolism

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Many organisms have metabolic pathways to synthesise and break down purines.

Synthesis

Purines are biologically synthesized as nucleosides (bases attached to ribose). The committed step is amidophosphoribosyltransferase.

Both adenine and guanine are derived from the nucleoside inosine monophosphate (IMP), which is synthesised on a pre-existing ribose through a complex pathway using atoms from the amino acids glycine, glutamine, and aspartic acid, as well as formate ions transferred from the coenzyme tetrahydrofolate.

GMP

AMP

Degradation

Purines from food (or from tissue turnover) are metabolised by several enzymes:

Guanine

Adenine

High levels of uric acid can predispose to gout when the acid crystalises in joints; this phenomenon only happens in humans and some animal species (e.g. dogs) that lack an intrinsic uricase enzyme that can further degrade uric acid into 5-Hydroxyisourate.

Salvage

Purines from turnover of nucleic acids (or from food) can also be salvaged and reused in new nucleotides.

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