The conjugation (esterification) of bilirubin occurs in the hepatocytes by the enzyme uridyldiphosphate glucuronyl transferase (UDPGT)
The enzyme transfers a glucuronic acid molecule to bilirubin to form bilirubin diglucuronide, known as conjugated bilirubin.
Intestinal bacteria can change Conj. bili. to be urobilinogen
(colorless product)