Biosynthesis of Bilirubin Glucuronide

It has now been established that in common with many other glu-curonides, bilirubin glucuronide can be synthesized in the adult rat, rabbit, mouse, and guinea pig liver by the enzymatic transfer of glucuronic acid from uridine diphosphate glucuronic acid to an acceptor substance, namely, bilirubin (Fig. 3) (B17, G5, L3, L5, S8). The transferring enzyme (glucuronyl transferase) has been shown by Schmid et al. 

Preliminary studies by Arias et al. (A5) using 4-methylumbelliferone as a substrate indicate that glucuronides can also be synthesized from a-glucuronic acid-1-phosphate by an enzyme system present in the soluble fraction of rat liver homogenates. It is not yet known whether such a system is capable of conjugating bilirubin. 

In complementary experiments Billing and Weinbren (cited in BIO) infused bilirubin in amounts sufficient to saturate the capacity of the liver to excrete the pigment and noted that, in addition to bilirubin, pigment I but no pigment II accumulated in the plasma. The liver poisons ethionine and icterogenin also cause an accumulation of pigment I but not of pigment II in the blood of experimental animals (B13). 

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