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

# Glucose–alanine cycle

Muscle sends its spare nitrogen to the liver as alanine; the liver turns it into urea and sends back glucose.

Updated 2026-11-01

## Key facts

- In muscle, alanine aminotransferase (ALT) moves the amino group from glutamate to pyruvate: alanine forms.
- In the liver, ALT returns the amino group to α-ketoglutarate; the nitrogen goes to the urea cycle and the pyruvate to gluconeogenesis.
- It carries nitrogen and carbon together, with no free ammonia in the blood.
- It dominates in fasting and prolonged exercise, when muscle breaks down protein.

## In detail

- 1. Muscle proteins are broken down; amino acids hand their amino group to α-ketoglutarate, forming glutamate.
- 2. Muscle ALT transfers that amino group to pyruvate from glycolysis: alanine.
- 3. Alanine travels in the blood to the liver.
- 4. Liver ALT turns it back into pyruvate and forms glutamate; glutamate releases ammonia, which enters the urea cycle.
- 5. The pyruvate goes through gluconeogenesis and the glucose returns to muscle.

**Also called**
Cahill cycle

## Clinical notes

- Blood ALT (formerly SGPT) is a sensitive marker of liver damage because it is abundant in hepatocytes.
- ALT needs pyridoxal phosphate (B6).
- In liver failure nitrogen is not cleared as urea and ammonia rises (hepatic encephalopathy).

## Pathways

- [Gluconeogenesis](https://durgical.com/en/biochemistry/pathways/gluconeogenesis/)
- [Glycolysis](https://durgical.com/en/biochemistry/pathways/glycolysis/)

## Related conditions

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

## Related

- [Pyruvate](https://durgical.com/en/biochemistry/molecules/pyruvate/)
- [Glucose](https://durgical.com/en/biochemistry/molecules/glucose/)
- [Cori cycle](https://durgical.com/en/biochemistry/topics/cori-cycle/)
- [Krebs cycle (citric acid cycle)](https://durgical.com/en/biochemistry/pathways/krebs-cycle/)

## Test yourself

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

## Which enzyme makes alanine from pyruvate in muscle?

Alanine aminotransferase (ALT), with pyridoxal phosphate (B6).

## What advantage does the glucose–alanine cycle have over the Cori cycle?

Besides carbon it carries nitrogen to the liver without releasing toxic ammonia into the blood.

## What happens to alanine's nitrogen in the liver?

It goes to glutamate and then into the urea cycle; it leaves in the urine as urea.

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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); [Gluconeogenesis](https://reactome.org/PathwayBrowser/#/R-HSA-70263) (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.

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