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[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# Hypoxanthine

Hypoxanthine is a purine the cell can either recycle (HGPRT) or break down to uric acid (xanthine oxidase).

Updated 2026-11-01

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## Key facts

- It is formed from inosine by purine nucleoside phosphorylase.
- Crossroads: HGPRT + PRPP → IMP (salvage) or xanthine oxidase → xanthine (breakdown).
- Allopurinol is an isomer of hypoxanthine (one nitrogen moves position).
- It is the base of IMP and inosine.

**Formula**
C₅H₄N₄O

**PubChem**
[CID 135398638](https://pubchem.ncbi.nlm.nih.gov/compound/135398638)

## Structure

- A purine with an oxo group at C6 (6-oxopurine).

## Clinical notes

- On allopurinol, hypoxanthine and xanthine accumulate; together they are more soluble than uric acid alone.
- It rises in xanthinuria and in HGPRT deficiency.

## Pathways

- [Purine degradation and salvage](https://durgical.com/en/biochemistry/pathways/purine-degradation-and-salvage/)

## Related conditions

- [Hereditary xanthinuria](https://durgical.com/en/conditions/hereditary-xanthinuria/)
- [Lesch-Nyhan syndrome](https://durgical.com/en/conditions/lesch-nyhan-syndrome/)

## Related

- [Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)](https://durgical.com/en/biochemistry/enzymes/hypoxanthine-guanine-phosphoribosyltransferase/)
- [Xanthine oxidase](https://durgical.com/en/biochemistry/enzymes/xanthine-oxidase/)
- [IMP (inosine monophosphate)](https://durgical.com/en/biochemistry/molecules/imp/)
- [Uric acid](https://durgical.com/en/biochemistry/molecules/uric-acid/)
- [Adenosine deaminase (ADA)](https://durgical.com/en/biochemistry/enzymes/adenosine-deaminase/)

## Test yourself

Think of the answer, then tap the question to see it.

## What are the two fates of hypoxanthine?

Salvage to IMP by HGPRT, or breakdown to xanthine and uric acid by xanthine oxidase.

## Which drug is an isomer of hypoxanthine?

Allopurinol, which inhibits xanthine oxidase.

## Which enzyme releases hypoxanthine from inosine?

Purine nucleoside phosphorylase (PNP), using phosphate.

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Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Hypoxanthine (CID 135398638)](https://pubchem.ncbi.nlm.nih.gov/compound/135398638) (PubChem, NCBI, 2026) · Public domain; [Purine salvage](https://reactome.org/PathwayBrowser/#/R-HSA-74217) (Reactome, 2026); [Purine catabolism](https://reactome.org/PathwayBrowser/#/R-HSA-74259) (Reactome, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/molecules/hypoxanthine/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/molecules/hypoxanthine/