Porphins and Bile Pigments

Little is known of the destruction of the porphins themselves. Hema-toporphin when injected is excreted in the bile. Coproporphin, because of its relatively greater solubility, is excreted in the urine and also in the bile (146). Injection of 100 mg. of protoporphin into bile fistula dogs resulted in the excretion of only 1 mg. (156a), possibly indicating destruction of the porphin. Kench (76) has recently found that, when coproporphin I is incubated with yeast under conditions in which coproporphin is known to be synthesized, it disappears, suggesting that the amount of coproporphin isolated from yeast at any one time is determined not only by the rate of production, but also by the rate of destruction of the porphin. 

The reduction of biliverdin to bilirubin was shown to take place in the presence of liver brei (13). Baumgartel (14) claims that reduction by liver brei, especially in the presence of cysteine, secondary phosphate, and glucose, can be carried so far that even the pyrrole reaction is no longer positive. It is interesting to note that the reduction of biliverdin to bilirubin 

Watson (154) suggests that they may be identical with copronigrin and that similar products can be obtained by the oxidation of urobilin and stercobilin. 

In icteric urine, colorless dipyrroles, propentdyopents, were found (14a). The structures postulated for them by Fischer and Dobeneck are  

When this urine was treated with alkali and dithionite a red color was produced. The red pigments, pentdyopents, have an absorption band in the neighborhood of 525 xa.fi] they are salts which autoxidize very readily to colorless forms, and they also become colorless in very weak acids. Pro-pentdyopent was isolated from gall stones as colorless crystals by Fischer and Dobeneck (33a) and was found to consist of two dipyrroles, differing in side chain composition, and derivable from bilirubin by oxidation. 

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