Which enzyme catalyzes the conjugation of bilirubin with glucuronic acid?

Which enzyme catalyzes the conjugation of bilirubin with glucuronic acid?

• A. Leucine aminopeptidase
• B. Glucose-6-phosphate dehydrogenase
• C. Uridine diphosphate glucuronyltransferase
• D. Carbamoyl phosphate synthetase

Answer: (C)

Conjugating bilirubin with glucuronic acid is a Phase II detoxification step in the liver. This reaction is carried out by UDP-glucuronosyltransferase, which transfers glucuronic acid from UDP-glucuronic acid to bilirubin to form bilirubin diglucuronide. This modification makes bilirubin water-soluble, allowing it to be excreted in bile. The other enzymes listed have different roles—one is a protease that trims amino acids from peptides, another generates NADPH in the pentose phosphate pathway, and the last helps synthesize carbamoyl phosphate for the urea cycle and pyrimidine biosynthesis. Thus, the enzyme that catalyzes bilirubin glucuronidation is UDP-glucuronyltransferase.

Conjugating bilirubin with glucuronic acid is a Phase II detoxification step in the liver. This reaction is carried out by UDP-glucuronosyltransferase, which transfers glucuronic acid from UDP-glucuronic acid to bilirubin to form bilirubin diglucuronide. This modification makes bilirubin water-soluble, allowing it to be excreted in bile. The other enzymes listed have different roles—one is a protease that trims amino acids from peptides, another generates NADPH in the pentose phosphate pathway, and the last helps synthesize carbamoyl phosphate for the urea cycle and pyrimidine biosynthesis. Thus, the enzyme that catalyzes bilirubin glucuronidation is UDP-glucuronyltransferase.