One step: the free base takes a ribose phosphate from PRPP
Route: Hypoxanthine + 5-Phosphoribosyl 1-pyrophosphate → Inosine monophosphate
Cells reuse purine bases instead of building new rings. Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) moves the ribose 5-phosphate of PRPP onto hypoxanthine and releases pyrophosphate. The product is IMP, which is the branch point to AMP and GMP. The same enzyme acts on guanine, shown in the next pathway. Loss of HGPRT in humans causes Lesch-Nyhan syndrome.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Hypoxanthine-guanine phosphoribosyltransferase | 2.4.2.8 | PPᵢ |
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).