Purine interconversion and degradation in humans

Using abbreviated structural diagrams, this figure schematically shows the two purine nucleotides (adenosine monophosphate and guanosine monophosphate), nucleosides (adenosine and guanosine), and bases (adenine and guanine) as well as the corresponding intermediary molecules (inosine monophosphate, inosine, and hypoxanthine). All endogenously produced and dietary purines share the same final pathway of degradation: via inosine, hypoxanthine, xanthine, and urate/uric acid. The enzyme xanthine oxidase, which catalyzes two steps in this process, is inhibited by the drugs allopurinol and febuxostat. The enzymes hypoxanthine-guanine phosphoribosyltransferase (HPRT) and adenine phosphoribosyltransferase (APRT) catalyze salvage of purine bases by recycling them to ribonucleotides without increased net purine synthesis.