Final answer:
UDP-glucuronyl transferase (UDPG-T) is needed to convert unconjugated bilirubin into conjugated bilirubin. In the liver, bilirubin is conjugated with glucuronic acid by UDPG-T to form water-soluble bilirubin diglucuronide.
Step-by-step explanation:
To convert unconjugated bilirubin into conjugated bilirubin, the enzyme UDP-glucuronyl transferase (UDPG-T) is needed. In the liver, bilirubin is taken up and conjugated with glucuronic acid by UDPG-T to form bilirubin monoglucuronide and then bilirubin diglucuronide, which are water-soluble and can be easily excreted out.