Bilirubin diglucuronides

Figure 32-13. Structure of bilirubin diglucuronide (conjugated, "direct-reacting" bilirubin). Glucuronic acid is attached via ester linkage to the two propionic acid groups of bilirubin to form an acylglucuronide.

FIGURE 7.3 Structures of bilirubin diglucuronide and the 3- and 6-glucuronides of morphine. 

B22. Brodersen, R., Bilirubin diglucuronide in normal human blood serum. Scand. J. Clin. Lab. Invest. 18, 361-379 (1966). 

L12. Lucassen, J., The diazo reaction of bilirubin and bilirubin diglucuronide. Ph.D. Thesis, 76 pp. TJniv. of Utrecht, 1961. 

Excretion of bilirubin into bile Bilirubin diglucuronide is actively transported against a concentration gradient into the bile canaH culi and then into the bile. This energy-dependent, rate-limiting step is susceptible to impairment in liver disease. Unconjugated bilirubin is normally not excreted. 

Catabolism of heme 0 = bilirubin EB = bilirubin diglucuronide E = urobilinogen QE = urobilin A = stercobilin. 

Glucose may form glucuronic acid. A major function of glucuronic acid is to make lipid compounds more water soluble (e.g., bilirubin diglucuronide). 

C. Bilirubin is produced by oxidation of heme after its iron is released CO is released in this reaction. Bilirubin diglucuronide is excreted into the bile by the liver. 

A) a decrease in the rate of formation of bilirubin diglucuronides in the liver... 

B) an increase in the rate of secretion of bilirubin diglucuronides into the gallbladder... 

Formation of bilirubin diglucuronide. Glucuronidation occurs in two steps via formation of monoglucuronide. Mono-and diglucuronides are more water-soluble and less lipophilic than bilirubin. Conversion of bilirubin to water-soluble products is obligatory for excretion of bilirubin from hepatocytes. M, Methyl V, vinyl UPD-GA, UDP-glucuronic acid. 

The answer is d. (Murray, pp 359-374. Scriver, pp 2961-3104. Sack, pp 121-138. Wilson, pp 287—317.) Once bile is excreted into the gut, bilirubin diglucuronide is hydrolyzed and reduced by bacteria to form urobilinogen, which is colorless. Much of the urobilinogen of the stools is further oxidized by intestinal bacteria to stercobilin, which gives stools their characteristic brown color. Some urobilinogen is reabsorbed by the gut into the portal blood, transported to the kidney and converted and excreted as urobilin, which gives urine its characteristic yellow color. 

Heme -> Biliverdin -> Bilirubin -> (passage through blood to liver as bilirubin-albumin complex) -> Bilirubin diglucuronide -> excretion. 

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