458 



X. BILE PIGMENT FORMATION, ETC. 



In contradistinction to these esters, the "green hemin" itself was 

 found to contain iron in complex combination, which was not remov- 

 able by alkali. It was found to be a pyridine hemochrome which in 

 many ways behaved similarly to a pyridine hemochrome of the 

 porphj'rin type. There was, however, the remarkable difference that 

 its iron could be much more readily detached, e.g., by acids. The 

 course of reaction shown in Figure 2 was postulated. 



M « V 



protohemochrome 



M H V 



verdohemochrome 



M HH V 



biliverdin 



Fig. 2.. Formation of verdohemochrome and biliverdin from protohemochrome. 



It was suggested by Lemberg (1681,1682) that the formation of 

 bile pigments in the animal body proceeded in a similar way. The 

 oxidative opening of the porphyrin ring occurs before the removal of 

 iron and of the nitrogenous substance bound to it. In this way the 

 iron becomes easily detachable and biliverdin is formed. This is 

 subsequently reduced to bilirubin by enzyme systems of the cell, 

 which were studied by Lemberg and Wyndham (1715). 



The oxidation of the porphyrin ring begins with the replacement of 

 a methene group by ^ C — OH leading to the hemichrome of an 

 oxy porphyrin (cf. Chapter III, Section 8.2., and Chapter V, Section 

 8.3.). This was discovered by Lemberg and co-workers (1696,1698) 

 and later confirmed by Libowitzky and Fischer (1732). 



In the first preliminary note of Lemberg and co-workers (1695), the 

 oxyporphyrin hemichrome had been assumed to be a hydrogen peroxide 

 compound of protohemochrome. The error was rectified when the difference 

 between oxyporphyrin hemochrome and protohemochrome was discovered 

 (1698). 



In the presence of ascorbic acid and the absence of atmospheric 

 oxygen, very dilute hydrogen peroxide formed oxyporphyrin hemo- 

 chrome from pyridine hemochrome; hemochromes more stable to 



