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.
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
Related conditions
Related
- Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
- PRPP (phosphoribosyl pyrophosphate)
- Xanthine oxidase
Test yourself
Think of the answer, then tap the question to see it.
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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: APRT: Adenine phosphoribosyltransferase (human) (UniProt, 2026); Adenine phosphoribosyltransferase deficiency: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); APRT gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); 1ZN8: Human Adenine Phosphoribosyltransferase Complexed with AMP, in Space Group P1 at 1.76 A Resolution (RCSB Protein Data Bank, 2026).
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