[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Alanine aminotransferase (ALT, GPT)

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

# Alanine aminotransferase (ALT, GPT)

ALT moves the amino group of alanine to α-ketoglutarate. Measured in blood, it is the most used marker of liver damage.

Updated 2026-11-01

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## Key facts

- Alanine + α-ketoglutarate ⇌ pyruvate + glutamate; reversible.
- Its coenzyme is pyridoxal phosphate (vitamin B6).
- It sits mostly in the hepatocyte cytosol: more liver-specific than AST.
- It is central to the glucose–alanine cycle between muscle and liver.

**EC number**
[2.6.1.2](https://www.enzyme-database.org/query.php?ec=2.6.1.2)

**Genes**
GPT

**Structure (PDB)**
[3IHJ](https://www.rcsb.org/structure/3IHJ)

## Structure

- 3IHJ is human ALT2 (GPT2 gene) with PLP; serum ALT1 runs the same reaction.

## Regulation

- Glucocorticoids and fasting raise its expression in the liver.

## Inhibitors and toxins

- Cycloserine and aminooxyacetate, inhibitors of PLP enzymes (experimental).

## Clinical notes

- Very high ALT (more than 10 to 20 times normal): acute viral hepatitis, liver ischaemia or toxins such as paracetamol.
- In viral hepatitis and fatty liver it is usually higher than AST.
- B6 deficiency can give falsely low values.

## Related conditions

- [Viral hepatitis](https://durgical.com/en/conditions/viral-hepatitis/)
- [Cirrhosis](https://durgical.com/en/conditions/cirrhosis/)

## Related

- [Alanine](https://durgical.com/en/biochemistry/molecules/alanine/)
- [Pyruvate](https://durgical.com/en/biochemistry/molecules/pyruvate/)
- [Glutamate (glutamic acid)](https://durgical.com/en/biochemistry/molecules/glutamate/)
- [Aspartate aminotransferase (AST, GOT)](https://durgical.com/en/biochemistry/enzymes/aspartate-aminotransferase/)
- [Transamination and deamination](https://durgical.com/en/biochemistry/topics/transamination-and-deamination/)

## Test yourself

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

## Which reaction does ALT catalyse?

It moves the amino group of alanine to α-ketoglutarate, forming pyruvate and glutamate; it is reversible.

## Why is ALT more liver-specific than AST?

It is found mainly in the hepatocyte cytosol, whereas AST is also abundant in heart, muscle and red cells.

## Which vitamin forms its coenzyme?

B6, as pyridoxal phosphate, which carries the amino group from one substrate to the other.

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

Sources: [GPT: Alanine aminotransferase 1 (human)](https://www.uniprot.org/uniprotkb/P24298/entry) (UniProt, 2026); [Alanine transaminase (ALT) blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003473.htm) (MedlinePlus, US National Library of Medicine, 2026); [3IHJ: Human alanine aminotransferase 2 in complex with PLP](https://www.rcsb.org/structure/3IHJ) (RCSB Protein Data Bank, 2026).

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