In vivo, bilirubin circulates in the plasma and is taken up by hepatocytes and conjugated to one or two glucuronic acids in a reaction catalyzed by UDP glucuronidase to form bilirubin mono or diglucuronide. This water-soluble form is then excreted from the liver in bile in the feces or is converted to urobilinogen and excreted in the urine. In addition to aiding in the disposal of heme, bilirubin and its conjugated derivatives have been shown to exhibit anti-oxidant and antimutagenic effects and to play a role in gut barrier function.