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

# Adenine phosphoribosyltransferase (APRT)

Recycles free adenine; when it is missing, adenine turns into an insoluble compound that forms kidney stones.

Updated 2026-11-01

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## Key facts

- Adenine + PRPP → AMP + PPi.
- Autosomal recessive deficiency: xanthine oxidase oxidises adenine to 2,8-dihydroxyadenine (2,8-DHA), which is very insoluble.
- 2,8-DHA stones are radiolucent and are mistaken for uric acid stones.
- Blood uric acid is normal: the key is to identify the crystal in urine.

**EC number**
[2.4.2.7](https://www.enzyme-database.org/query.php?ec=2.4.2.7)

**Genes**
APRT

**Structure (PDB)**
[1ZN8](https://www.rcsb.org/structure/1ZN8)

## Regulation

- Depends on adenine and PRPP supply; no relevant allosteric regulation.

## Inhibitors and toxins

- None in clinical use

## Clinical notes

- APRT deficiency causes stones and crystal nephropathy from 2,8-DHA, which can lead to chronic kidney disease.
- It is treated with xanthine oxidase inhibitors (allopurinol or febuxostat), which prevent 2,8-DHA formation.
- Unlike uric acid stones, 2,8-DHA stones do not dissolve when urine is alkalinised.

## Pathways

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

## Related conditions

- [Kidney stones (urolithiasis)](https://durgical.com/en/conditions/kidney-stones/)
- [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/)

## Related

- [Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)](https://durgical.com/en/biochemistry/enzymes/hypoxanthine-guanine-phosphoribosyltransferase/)
- [PRPP (phosphoribosyl pyrophosphate)](https://durgical.com/en/biochemistry/molecules/prpp/)
- [Xanthine oxidase](https://durgical.com/en/biochemistry/enzymes/xanthine-oxidase/)

## Test yourself

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## Which compound forms the stones in APRT deficiency?

2,8-Dihydroxyadenine, made by xanthine oxidase from unrecycled adenine.

## Why does allopurinol help in APRT deficiency?

It blocks xanthine oxidase, the enzyme that turns adenine into insoluble 2,8-DHA.

## How do 2,8-DHA stones look on a plain X-ray?

They are not seen: they are radiolucent, like uric acid stones.

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

Sources: [APRT: Adenine phosphoribosyltransferase (human)](https://www.uniprot.org/uniprotkb/P07741/entry) (UniProt, 2026); [Adenine phosphoribosyltransferase deficiency: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/adenine-phosphoribosyltransferase-deficiency/) (MedlinePlus, US National Library of Medicine, 2026); [APRT gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/aprt/) (MedlinePlus, US National Library of Medicine, 2026); [1ZN8: Human Adenine Phosphoribosyltransferase Complexed with AMP, in Space Group P1 at 1.76 A Resolution](https://www.rcsb.org/structure/1ZN8) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/enzymes/adenine-phosphoribosyltransferase/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/adenine-phosphoribosyltransferase/