Tauroconjugated

Tauroconjugated describes a molecule that has taurine attached through a covalent bond, most often referring to bile acids that have been conjugated with taurine to form tauro-conjugated bile acids, or bile salts.

Biosynthesis and purpose

In the liver, bile acids are activated as bile acid–CoA thioesters and then conjugated with taurine by the enzyme bile acid–CoA:amino acid N-acyltransferase (BAAT). The resulting tauro-conjugated bile acids are secreted into bile and contribute to the pool of bile salts that aid digestion. Conjugation with taurine increases the water solubility of bile acids and stabilizes them in the harsh conditions of bile, facilitating their emulsifying action in the small intestine.

Examples

Common tauro-conjugated bile acids include taurocholic acid (taurocholate), taurochenodeoxycholic acid (TCDCA), and taurolithocholic acid (TLCA). Other tauro-conjugated bile acids exist, alongside glyco-conjugated counterparts such as glycocholic acid, which are formed with glycine.

Physiology and transport

Tauro-conjugated bile acids are part of the enterohepatic circulation. They are secreted into bile, stored in the gallbladder, and released into the intestine after meals. In the ileum, they are reabsorbed primarily via the apical sodium-dependent bile acid transporter (ASBT) and returned to the liver through the portal vein, where they can be reconjugated or recycled.

Variability and clinical relevance

Conjugation with taurine is more prominent in certain species; humans produce both tauro- and glyco-conjugated bile acids, with the relative proportions varying. Alterations in bile acid conjugation can occur in liver disease or metabolic disorders, affecting solubility, detergent properties, and enterohepatic recycling. Tauroconjugated compounds thus play a central role in fat digestion and bile acid homeostasis.