Taurine: the pathway in the body

This page shows the biochemical pathway behind the laboratory value Taurine: which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Taurine is a sulfur-containing amino sulfonic acid that the body makes from cysteine and also absorbs from food. It is attached to bile acids and, as a dissolved substance, regulates the water balance of cells.

The pathway step by step

1. Methionine → Cysteine CBS and CSE · Vitamin B6 (PLP) Two enzymes with vitamin B6 as cofactor, cystathionine β-synthase and cystathionine γ-lyase, convert homocysteine via cystathionine into cysteine. Source 1
2. Cysteine → Cysteine sulfinic acid Cysteine dioxygenase · Iron, oxygen Cysteine dioxygenase attaches two oxygen atoms to the sulfur. The enzyme contains iron and controls how much cysteine flows towards taurine. Source 1, 2
3. Cysteine sulfinic acid → Hypotaurine CSAD (decarboxylase) · Vitamin B6 (PLP) Cysteine sulfinic acid decarboxylase removes the carboxyl group; it too works with pyridoxal phosphate, the active form of vitamin B6. Source 2, 3
4. Hypotaurine → Taurine FMO1 · NADPH, oxygen The flavin monooxygenase FMO1 oxidises hypotaurine to taurine. In addition, a large share of the body’s taurine comes directly from meat, fish and seafood. Source 3
5. Taurine in the blood → In the liver cell In the liver, taurine is attached to bile acids. Source 4
6. Taurine in the blood → In other cells In muscle, heart, retina and white blood cells, taurine is present in large amounts in free, dissolved form and is not built into proteins. Source 5
7. Cholyl-CoA → Taurocholic acid BAAT The enzyme BAAT attaches taurine to the bile acid. As a result the bile salt stays dissolved even in the acidic small intestine. Source 4
8. Taurocholic acid → Bile · BSEP transporter The bile salts reach the gut with the bile. There they coat fat droplets so that the enzymes of the pancreas can act on them. Source 4
9. In other cells → Osmolyte in the cell Taurine is one of the osmolytes: when a cell swells, it releases taurine through dedicated channels and water follows. In this way the cell restores its volume. Source 5

Cofactors in this pathway

• Vitamin B6 (PLP) — Cofactor of CBS and CSE on the way to cysteine, and of cysteine sulfinate decarboxylase Source 1, 2In the ORY catalogue as a laboratory value: Vitamin B6
• Iron — Metal at the active site of cysteine dioxygenase Source 1In the ORY catalogue as a laboratory value: Eisen
• Methionine — Supplies, via transsulfuration, the sulfur contained in taurine Source 1In the ORY catalogue as a laboratory value: Methionin
• Vitamin B2 (FAD) — Component of the flavin monooxygenase FMO1, which oxidises hypotaurine to taurine Source 3
• Coenzyme A — Activates bile acids before BAAT attaches taurine Source 4
• Sodium — The transporter TauT carries taurine into the cell together with sodium and chloride Source 2, 5In the ORY catalogue as a laboratory value: Natrium (intrazellulär)

Sources

1. Stipanuk MH, Ueki I. Dealing with methionine/homocysteine sulfur: cysteine metabolism to taurine and inorganic sulfur. J Inherit Metab Dis 2011 · PubMed 20162368
2. Tappaz ML. Taurine biosynthetic enzymes and taurine transporter: molecular identification and regulations. Neurochem Res 2004 · PubMed 14992266
3. Miyazaki T. Identification of a novel enzyme and the regulation of key enzymes in mammalian taurine synthesis. J Pharmacol Sci 2024 · PubMed 38081683
4. Russell DW. The enzymes, regulation, and genetics of bile acid synthesis. Annu Rev Biochem 2003 · PubMed 12543708
5. Pasantes-Morales H. Taurine Homeostasis and Volume Control. Adv Neurobiol 2017 · PubMed 28828605

Related pathways

• Methylation: methionine and homocysteine — methionine
• Bile acids — bile
• Glutathione — cysteine
• Vitamin B12 — methionine
• Carnitine — Vitamin B6, Eisen

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