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.
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
Related
- Alanine
- Pyruvate
- Glutamate (glutamic acid)
- Aspartate aminotransferase (AST, GOT)
- 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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: GPT: Alanine aminotransferase 1 (human) (UniProt, 2026); Alanine transaminase (ALT) blood test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); 3IHJ: Human alanine aminotransferase 2 in complex with PLP (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.