The colon-handled oxidation of urobilinogen by microorganisms yields which breakdown product?

The colon-handled oxidation of urobilinogen by microorganisms yields which breakdown product?

• A. Porphobilinogen
• B. Urobilin
• C. Stercobilinogen
• D. Protoporphyrin

Answer: (B)

Colon bacteria transform bilirubin that enters the intestine into urobilinogen, which is colorless. When microorganisms in the colon oxidize urobilinogen, the immediate product formed is urobilin, a yellow pigment. Some urobilinogen can be further converted downstream to stercobilinogen and then stercobilin, which gives stool its brown color. The other substances listed are not the direct oxidation product of urobilinogen in the colon; porphobilinogen and protoporphyrin are different heme-related intermediates, and stercobilinogen is an intermediate toward stercobilin rather than the direct oxidation product of urobilinogen.

Colon bacteria transform bilirubin that enters the intestine into urobilinogen, which is colorless. When microorganisms in the colon oxidize urobilinogen, the immediate product formed is urobilin, a yellow pigment. Some urobilinogen can be further converted downstream to stercobilinogen and then stercobilin, which gives stool its brown color. The other substances listed are not the direct oxidation product of urobilinogen in the colon; porphobilinogen and protoporphyrin are different heme-related intermediates, and stercobilinogen is an intermediate toward stercobilin rather than the direct oxidation product of urobilinogen.