Which enzyme is responsible for the conjugation of bilirubin?

Which enzyme is responsible for the conjugation of bilirubin?

• A. UDP-glucuronyl transferase
• B. Alkaline phosphatase
• C. Glutamate dehydrogenase
• D. Leucine aminopeptidase

Answer: (A)

Bilirubin conjugation is the process of attaching glucuronic acid to bilirubin to make it water-soluble for biliary excretion. This reaction is catalyzed by the enzyme UDP-glucuronyl transferase (UGT1A1) in hepatocytes, which transfers glucuronic acid from UDP-glucuronic acid to bilirubin, forming bilirubin diglucuronide. Without this conjugation, bilirubin remains fat-soluble and cannot be efficiently eliminated. The other enzymes listed have different roles—alkaline phosphatase is a phosphatase, not a conjugating enzyme; glutamate dehydrogenase and leucine aminopeptidase participate in amino acid metabolism and proteolysis, not bilirubin conjugation.

Bilirubin conjugation is the process of attaching glucuronic acid to bilirubin to make it water-soluble for biliary excretion. This reaction is catalyzed by the enzyme UDP-glucuronyl transferase (UGT1A1) in hepatocytes, which transfers glucuronic acid from UDP-glucuronic acid to bilirubin, forming bilirubin diglucuronide. Without this conjugation, bilirubin remains fat-soluble and cannot be efficiently eliminated. The other enzymes listed have different roles—alkaline phosphatase is a phosphatase, not a conjugating enzyme; glutamate dehydrogenase and leucine aminopeptidase participate in amino acid metabolism and proteolysis, not bilirubin conjugation.