The events of human purine metabolism are conveniently, if somewhat arbitrarily, grouped into four pathways: de novo synthesis of inosine 5'-monophosphate (IMP), the biosynthesis of other purine ribo- and deoxyribonucleotides, purine salvage reactions, and purine catabolism (Watts 1974).
De novo synthesis of inosine 5'-monophosphate (IMP). The purine ribonucleotide IMP is assembled on 5-phospho-alpha-D-ribose 1-diphosphate (PRPP).
Purine biosynthesis [interconversion]. Purine ribo- and deoxyribonucleotide di- and triphosphates are synthesized, both from IMP and from guanosine and adenosine ribo- and deoxyribonucleotide monophosphates generated in salvage reactions.
Purine salvage reactions. Purine nucleosides and free bases generated by DNA and RNA breakdown are converted to nucleotide monophosphates.
Purine catabolism. The purine bases guanine and hypoxanthine are degraded to uric acid, which is excreted from the body.