464 



X. BILE PIGMENT FORMATION, ETC. 



turns a pure green (verdohemoglobin) with a sharp absorption band 

 at 665 miJL, while an excess of dithionite transforms it into a yellow 

 compound. The absorption spectrum of verdohem^'globin does not 

 differ from that of denatured globin verdohem?chrome, and when a 

 solution of verdohemoglobin is oxygenated verdohenuglobin results. 

 There is thus no evidence for the formation of a compound comparable 

 to oxyhemoglobin (1716,2309). 



2.4. Structure of Verdoheme 



The verdohemochrome formula shown in Figure 2 assumes it to 

 be an isobiliverdin iron complex in which pyrrole ring IV is in a 

 tautomeric form. This assumption was based on the facts that 

 treatment with acids yielded biliverdin and that sodium amalgam 

 reduced it to mesobilane. 



The latter experiment excluded the possibility that verdoheme 

 contained a tetrapyrrolic ring system closed by a carbonyl (CO) 

 group. Such a compound might perhaps have given bile pigments 

 on being split with acids, but would have given porphyrinogen, not 

 mesobilane on complete reduction. Nevertheless, Libowitzky and 

 Fischer (1731,1732) later assumed this structure again for verdohemo- 

 chrome. This was finally disproved by the conversion by Lemberg 

 (1687) of verdohemochrome into monoazahemochrome (cf. Chapter 

 V). This could be well understood with the verdohemochrome 

 formula as an isobiliverdin iron compound (Fig. 4). In spite of this 



NH, 



verdohemochrome monoazahemochrome 



Fig. 4. Reaction of verdohemochrome with ammonia. 



the assumption of a carbon closed ring was not abandoned by the 



Fischer school (2666,2667).* The iron, which is so labile in verdoheme 



* Pure verdohemochrome yielded no trace of porpliyrin when treated with formic 

 acid, palladium, and hydrogen in the manner l)y which Stier and Gangl (2607a) obtained 

 a small amount of coproporphyrin from "coproverdohemin" (16Sf<). 



