Alanin: the pathway in the body · Biomarker & Blood Analysis

Alanin is part of the pathway “Alanine”. This page shows the whole pathway; the station of Alanin is highlighted.

Where this laboratory value sits: Alanine — amino acid. Alanine aminotransferase (ALT) transfers an amino group from glutamate to pyruvate, forming alanine. The glutamate largely comes from the breakdown of leucine, isoleucine and valine in muscle. This is how muscle binds nitrogen. Source 1, 2, 3

In brief

Alanine is an amino acid the body can build itself. Muscle forms it from pyruvate and an amino group and sends it to the liver, which turns it back into glucose and urea. In this way nitrogen leaves muscle without free ammonium.

The pathway step by step

Each station states what the compound does there. Three signs: ↑ supplies — builds up or makes available · ↓ depletes — inhibits, consumes or withholds · ↕ both, depending on amount. Behind it stands what the statement rests on: established physiology, observed in studies, or contested. The signs do not grade; they name the direction.

1. Glucose → Pyruvate Glycolysis · NAD⁺ In glycolysis, glucose is broken down to pyruvate in several steps. The cell gains ATP in the process. Pyruvate is the carbon backbone that can accept an amino group. Source 4↑ supplies Pyruvate is a crossroads: it is broken down further in the mitochondria or accepts an amino group via ALT and becomes alanine. In the second case its carbon leaves the muscle. established physiology Source 4, 1
   ⚖ When the balance tips

   too much — If pyruvate builds up in muscle, ALT takes in more of it and transfers more amino groups from glutamate; more alanine forms.

   too little — If little pyruvate is available, ALT finds fewer acceptors for the amino group; muscle then releases its nitrogen more as glutamine.

   established physiology · Source 1, 2, 6

2. Pyruvate → Alanine ALT · Vitamin B6 (PLP), Glutamate Alanine aminotransferase (ALT) transfers an amino group from glutamate to pyruvate, forming alanine. The glutamate largely comes from the breakdown of leucine, isoleucine and valine in muscle. This is how muscle binds nitrogen. Source 1, 2, 3↑ supplies Alanine bundles an amino group and a carbon backbone in one molecule. In this way muscle passes on the nitrogen from the breakdown of leucine, isoleucine and valine in an easily transported form. established physiology Source 1, 2, 3
   ⚖ When the balance tips

   too much — If much alanine forms, muscle releases more of it into the blood. The ALT reaction is reversible and runs in one direction or the other depending on the supply of pyruvate and glutamate.

   too little — If little alanine forms, muscle hands on the amino groups by another route, mainly as glutamine.

   established physiology · Source 1, 2, 8

3. Alanine → Alanine in the blood The muscle releases alanine into the blood. By this route, carbon and nitrogen leave the muscle together without free ammonium being formed. In the liver, alanine supplies carbon for glucose and nitrogen for urea. Source 1, 2↑ supplies Alanine in the blood is a transport form: it carries carbon for gluconeogenesis and nitrogen for the urea cycle to the liver, without free ammonium forming on the way. established physiology Source 1, 2
   ⚖ When the balance tips

   too much — If more alanine reaches the liver, more pyruvate is available there for new glucose and more nitrogen for the urea cycle.

   too little — If little alanine arrives, the liver receives less carbon from muscle and builds new glucose more from lactate and glycerol.

   established physiology · Source 1, 4

4. Alanine in the liver → Pyruvate in the liver ALT · Vitamin B6 (PLP) In the liver the same reaction runs in reverse: ALT passes the amino group of alanine to α-ketoglutarate. Pyruvate remains. Here pyruvate is the starting point for new glucose. Source 1, 2↑ supplies In the liver, pyruvate is the starting point of gluconeogenesis: pyruvate carboxylase converts it with biotin, ATP and bicarbonate into oxaloacetate. established physiology Source 4, 9
   ⚖ When the balance tips

   too much — If pyruvate builds up, pyruvate carboxylase converts more of it into oxaloacetate; acetyl-CoA from fat breakdown additionally switches the enzyme on.

   too little — If little pyruvate is available, less oxaloacetate forms by this route and thus less new glucose.

   established physiology · Source 9, 4

5. Pyruvate in the liver → New glucose Pyruvate carboxylase · Biotin, ATP From pyruvate, the liver rebuilds glucose via gluconeogenesis. The first step, pyruvate carboxylase, needs biotin. The glucose enters the blood — the cycle is complete. During fasting it supplies the brain and muscle. Source 4, 1↑ supplies The new glucose enters the blood and supplies the brain, red blood cells and muscle during fasting. Part of it returns to muscle and yields pyruvate there again. established physiology Source 4, 1
   ⚖ When the balance tips

   too much — If the liver forms more glucose than is used, blood glucose rises; insulin then inhibits gluconeogenesis in the liver.

   too little — If the liver forms little new glucose, supply during fasting must come from its glycogen store; once that is empty, only gluconeogenesis remains.

   established physiology · Source 4

6. Alanine in the liver → Glutamate ALT · α-Ketoglutarate The amino group handed on ends up on α-ketoglutarate, which becomes glutamate. This is how nitrogen from the muscle arrives in the liver. Glutamate thus collects the amino groups of the liver cell. Source 2, 6↑ supplies Glutamate collects the amino groups in the liver cell. It passes them to glutamate dehydrogenase or, via aspartate, to the urea cycle. established physiology Source 6, 7
   ⚖ When the balance tips

   too much — If glutamate builds up, glutamate dehydrogenase releases more ammonium; at the same time more N-acetylglutamate forms from glutamate, which switches on the first step of the urea cycle.

   too little — If little α-ketoglutarate is available, less glutamate forms, and ALT takes over fewer amino groups from alanine.

   established physiology · Source 6, 7, 5

7. Glutamate → Ammonium Glutamate dehydrog. · NAD⁺ Glutamate dehydrogenase removes the amino group as ammonium and releases α-ketoglutarate, which is then available again. The liver processes it at once so that it does not accumulate in the blood. Source 5, 6↕ both, depending on amount Ammonium is the raw material for urea and glutamine. Free and in larger amounts it reaches the brain with the blood, where astrocytes bind it to glutamate; this is why the liver processes it at once. established physiology Source 6
   ⚖ When the balance tips

   too much — If ammonium builds up, the liver binds more of it as glutamine, and more enters the blood; in the brain, astrocytes then bind it into glutamine.

   too little — If little ammonium forms, the urea cycle runs more slowly; the nitrogen then stays bound in amino acids for longer.

   established physiology · Source 6, 7

8. Ammonium → Urea Urea cycle · ATP In the urea cycle, the liver cell incorporates ammonium into urea; the first step uses ATP. Urea dissolves readily in water and leaves the body via the kidney. In this way the nitrogen from muscle leaves the body. Source 7, 6↓ depletes Urea removes nitrogen from the body in a water-soluble, barely reactive form. Each molecule carries two nitrogen atoms: one from ammonium, one from aspartate. established physiology Source 7, 6
   ⚖ When the balance tips

   too much — If much protein is broken down, the liver forms more urea; the enzymes of the cycle adjust their amount to the protein supply over days.

   too little — If little urea is formed, more nitrogen stays in the blood as ammonium and glutamine.

   established physiology · Source 7, 6

Further stations

• Glucose — from the blood The muscle cell absorbs glucose from the blood or draws it from its own glycogen store. It is the fuel from which the backbone of alanine later forms. Source 1, 4↑ supplies Glucose is the fuel of the muscle cell. Via glycolysis it yields ATP and at the same time the pyruvate that later serves as the carbon backbone of alanine. established physiology Source 1, 4
  ⚖ When the balance tips

  too much — If plenty of glucose arrives, glycolysis forms more pyruvate; ALT then has more backbone available onto which it can transfer amino groups.

  too little — If little glucose arrives from the blood, the muscle cell draws on its glycogen store; once it is used up, less pyruvate forms from glucose.

  established physiology · Source 1, 4

• Alanine in the liver — drawn from the blood The liver cell absorbs alanine from the blood via its own transporters. Alanine is one of the main amino acids arriving there. There it serves mainly as a starting material for new glucose. Source 1↑ supplies In the liver, alanine is one of the main starting materials for new glucose. During fasting the liver draws particularly large amounts of alanine from the blood. established physiology Source 1, 4
  ⚖ When the balance tips

  too much — If the liver takes up much alanine, ALT, gluconeogenesis and the urea cycle work harder; more nitrogen becomes urea.

  too little — If the liver takes up little alanine, new glucose comes more from other starting materials, and less nitrogen from muscle reaches the urea cycle.

  established physiology · Source 1, 6

Cofactors in this pathway

• Vitamin B6 — As pyridoxal phosphate, cofactor of alanine aminotransferase (ALT) in muscle and liver; without PLP, ALT stalls Source 8In the ORY catalogue as a laboratory value: Vitamin B6
• Glutamate — Donates the amino group to pyruvate in muscle, forming alanine; nitrogen thus moves on Source 1, 2In the ORY catalogue as a laboratory value: Glutamat
• alpha-Ketoglutarate — Accepts the amino group of alanine in the liver, becoming glutamate; with little of it, the handover stalls Source 2, 5In the ORY catalogue as a laboratory value: Alpha-Ketoglutarat (2-Oxoglutarat)
• Leucine, isoleucine, valine — Their breakdown in muscle supplies the amino groups for glutamate and thus for alanine; from food and muscle protein Source 3In the ORY catalogue as a laboratory value: Leucin
• Biotin — Cofactor of pyruvate carboxylase, the first step of gluconeogenesis from pyruvate; without biotin no oxaloacetate Source 9
• Magnesium — Pyruvate carboxylase converts pyruvate with MgATP and bicarbonate into oxaloacetate; acetyl-CoA switches it on Source 9In the ORY catalogue as a laboratory value: Magnesium
• NAD⁺ — Accepts hydrogen at glutamate dehydrogenase in the liver; ammonium is released Source 5In the ORY catalogue as a laboratory value: NAD⁺ (Nicotinamidadenindinukleotid)

Sources

1. Felig P. The glucose-alanine cycle. Metabolism 1973 · PubMed 4567003
2. Palmer TN, Caldecourt MA et al. Alanine and inter-organ relationships in branched-chain amino and 2-oxo acid metabolism. Review. Biosci Rep 1985 · PubMed 3938302
3. Holeček M. Branched-chain amino acids in health and disease: metabolism, alterations in blood plasma, and as supplements. Nutr Metab (Lond) 2018 · PubMed 29755574
4. Rui L. Energy metabolism in the liver. Compr Physiol 2014 · PubMed 24692138
5. Treberg JR, Banh S et al. Intertissue differences for the role of glutamate dehydrogenase in metabolism. Neurochem Res 2014 · PubMed 23412807
6. Adeva MM, Souto G et al. Ammonium metabolism in humans. Metabolism 2012 · PubMed 22921946
7. Morris SM Jr. Regulation of enzymes of the urea cycle and arginine metabolism. Annu Rev Nutr 2002 · PubMed 12055339
8. Vanderlinde RE. Review of pyridoxal phosphate and the transaminases in liver disease. Ann Clin Lab Sci 1986 · PubMed 3008634
9. Jitrapakdee S, St Maurice M, Rayment I et al. Structure, mechanism and regulation of pyruvate carboxylase. Biochem J 2008 · PubMed 18613815

Whole pathway: Alanine

Related pathways

• GABA, glutamate and glutamine — glutamate
• Liver enzymes — alanine
• Vitamin B6 — alanine
• Helicobacter pylori — urea
• Glycine and serine — Vitamin B6, Glutamat

As of 2026-09-16. Draft, written by Claude to schema v2; sources checked in PubMed; expert approval pending
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