In the liver, bilirubin is conjugated by addition of?

In the liver, bilirubin undergoes conjugation primarily with glucuronic acid to form bilirubin diglucuronide, which is a water-soluble form of bilirubin. This process is essential for making bilirubin water-soluble, facilitating its excretion from the liver into the bile and consequently into the intestines. The conversion to a conjugated form reduces bilirubin's toxicity and increases its solubility, allowing for proper elimination from the body.

The conjugation reaction is catalyzed by an enzyme called UDP-glucuronosyltransferase, which transfers glucuronyl groups to bilirubin. This process is crucial for maintaining bilirubin levels within the body, as high levels of unconjugated bilirubin can lead to jaundice and other health issues.

The other options do not correctly reflect the biochemical process involved in bilirubin conjugation in the liver. Vinyl groups, methyl groups, and hydroxyl groups do not participate in the conjugation of bilirubin in this context, reaffirming that glucuronyl groups are indeed the correct and specific addition responsible for this vital biological process.