144 



IV. BILE PIGMENTS 



In order to explain the development of optical activity one would have to 

 postulate in any case optically active reducing systems; it appears more 

 likely that these are bacterial enzj'me systems rather than nonbacterial 

 reducers present in the bile (cf. Chapter XI). The full publication of the 

 experiments will have to be awaited before the matter can be judged further. 



6.5. Porphobilin 



By action of hydrochloric acid on "porphobilinogen," a chromogen found 

 in the urine of patients with acute porphyria (1^'ection 8.3.), Waldenstrom 

 {2911) obtained a urobilinoid substance which he called porphobilin. Por- 

 phobilin is ether-insoluble and probably urobilene-(b), i.e., a bilene with the 

 same side chains as uroporphyrin. It can be reduced to a bilane, which 

 differs from porphobilinogen in molecular weight and in its Ehrlich reaction. 

 According to Waldenstrom porphobilinogen, a dipyrrylmethane, yields both 

 porphobilin and uroporphyrin by the action of hydrochloric acid. 



Porphobilin differs from urobilins by being precipitated with zinc acetate 

 and by not giving a zinc salt with green fluorescence. 



6.6. Bilenediones and Bilenetetrols (Choletelins) 



As in the case of the biliviolinoid pigments (cf. Section 5.4.), urobilinoid 

 pigments are obtained by oxidation of bilatrienes. Their structure has been 

 discussed in Section 2.4. (cf. al.so Table III). 



Heynsius and Campbell (lJ(IS,12()f)) and Stokvis (2670) obtained a sub- 

 stance very similar to urobilin by the oxidation of bilirubin; a zinc complex 

 salt of a urobilinoid pigment was, for instance, formed by oxidation of an 

 ammoniacal solution of bilirubin by iodine in the presence of zinc salt. They 

 called this substance choletelin. At that time it appeared mysterious that 



HQ/ N g N 



H 



H 



C XT C M OH 

 H ^ O H 



A 



ME MP PMME 



HO 



A 



N / C N 



om|\ h 



H OM 



A A^A A^/\ /\ 



B 



N 



/\0M 

 H OM 



OH 



Fig. 2r.. Choletelins. 



"urobilin" should be formed from bilirubin by oxidation as well as by reduc- 

 tion. The phenomenon was confirmed by Barrensclieen and Weltmann 



