Which two amino acids conjugate primary bile acids?

• A. Taurine and glycine
• B. Methionine and cysteine
• C. Lysine and arginine
• D. Serine and threonine

Answer: (A)

Conjugation of primary bile acids with specific amino acids happens to boost their water solubility and aid fat digestion. In humans and many mammals, the primary bile acids—cholic acid and chenodeoxycholic acid—are conjugated with glycine or taurine to form bile salts (glyco-, tauro- forms). This coupling makes the bile acids more amphipathic and lowers their pKa, which helps them emulsify fats in the intestine. The two amino acids used for this conjugation are glycine and taurine, yielding glycocholate and taurocholate. Other amino acids listed are not used for this purpose in standard physiology, so they don’t form the conjugated bile salts that are essential for bile function. BAAT catalyzes this reaction in hepatocytes, linking the bile acid-CoA intermediate to the chosen amino acid.