Five steps: remove the phosphate, remove the amino group, remove the ribose, then oxidize twice
Route: AMP → Adenosine → Inosine → Hypoxanthine → Xanthine → Uric acid
A 5'-nucleotidase removes the phosphate from AMP to give adenosine. Adenosine deaminase adds water and releases ammonium, which gives inosine. Purine nucleoside phosphorylase cleaves the bond to ribose with phosphate rather than water, so the products are the free base hypoxanthine and ribose 1-phosphate. Xanthine oxidoreductase then oxidizes hypoxanthine to xanthine and xanthine to uric acid. In the oxidase form the electrons go to O₂, which gives H₂O₂. Uric acid is the end product of purine breakdown in humans. Humans lack uricase, the enzyme that converts uric acid to allantoin. Too much uric acid crystallizes in joints as gout, and allopurinol treats gout by blocking xanthine oxidoreductase. A lack of adenosine deaminase causes some forms of severe combined immunodeficiency. Hypoxanthine can also return to IMP through the salvage pathway. AMP can also be deaminated to IMP first, which is left out here.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | 5'-Nucleotidase (CD73) | 3.1.3.5 | H₂O | Pᵢ |
| 2 | Adenosine deaminase | 3.5.4.4 | H₂O | NH₄⁺ |
| 3 | Purine nucleoside phosphorylase | 2.4.2.1 | Pᵢ | Ribose 1-phosphate |
| 4 | Xanthine oxidoreductase | 1.17.3.2 | O₂, H₂O | H₂O₂ |
| 5 | Xanthine oxidoreductase | 1.17.3.2 | O₂, H₂O | H₂O₂ |
Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).