TRANSFORMATION OF BILIRUBIN TO UROBILIN 551 



rubin. Theoretically, mesobilirubin (with reduction of the side chains 

 only) and mesobilane (with reduction of the side chains and addition 

 of four hydrogen atoms to the tetrapyrrolic system) may be inter- 

 mediates. Watson (2989, p. 2486) found some evidence for meso- 

 bilirubin occurring in the small intestine and assumed that it was 

 formed there and further reduced in the large intestine; he also 

 assumed mesobilane to be an intermediate of the reduction to tetra- 

 hydromesobilane in the intestine. From the investigations of Baum- 

 gartel (193,194), there is little doubt, however, that intestinal bacteria 

 reduce bilirubin directly to tetrahydromesobilane, while mesobilane 

 is formed by enzymic reduction of bilirubin in the liver. 



9.1.2. Formation of Urobilin in the Intestine. It is now gen- 

 erally agreed that the transformation of bilirubin into urobilin 

 occurs mainly in the intestine. In his classical experiments von 

 Miiller (199Jf) showed that urobilin disappears from the intestine 

 after obstruction of the bile duct, but reappears if pig's bile is fed 

 by stomach tube. Pig bile contains bilirubin, not urobilin, though 

 urobilinogen may have been overlooked (3030). Mtiller's results 

 were confirmed by McMaster and Elman (673,1827) with the bile 

 fistula technique of Rous and McMaster (237 4)- Heilmeyer and 

 co-workers (260) found that, after removal of the intestine, intrave- 

 nous injection of hemoglobin failed to produce urobilinuria in the 

 dog. Salen and Enochsson (2417) showed that laxatives decrease 

 urobilinuria in hemolytic jaundice, while constipation increases it 

 (209,1206,1829,2109,2110,2112,2380,2384,2565,3082; 2989, p. 2500). 

 The site of urobilin formation is largely the large intestine. The 

 theory of urobilin formation has been discussed in numerous reviews 

 (14,697,981,1301,1829,1932,2380,2384,2416,2417,2989,3082). 



Action of Intestinal Bacteria. As early as 1871 Maly (1854) 

 assumed that urobilin is formed by the action of intestinal bacteria 

 on bilirubin. In 1892 von Miiller found that the transformation 

 could be carried out with feces in peptone solution in an atmosphere 

 of hydrogen. The bacterial systems in feces which are responsible 

 for the reaction have been studied by Kammerer and IVIiller (1450, 

 1453,1454), Passini (2114,2115) and Baumgartel (193). 



Kammerer found that a synergism of the anaerobic Bacillus putrificus 

 Bienstock* with facultative aerobes (Escherichia coli or Vibrio) was required 

 which was active at a pH between 6.5 and 7.6; Passini found that B. putrificus 



* Clostridium lentoputrescens (?). The identity has not been ascertained. 



