CHAPTER IV 



BILE PIGMENTS 



1. INTRODUCTION 



1.1. Definition 



The term "bile pigments" or "bilinoid pigments" is today no 

 longer applied to all pigments found in the bile of animals or derived 

 from such pigments, but to a particular class of pyrrolic compounds 

 (tetrapyrrane derivatives). Thus although it occurs in the bile of 

 herbivorous animals, phylloerythrin (previously called bilipurpurin 

 or still more unsuitably cholehaematin) is no longer included in this 

 class since it is a porphyrin derived from chlorophyll. On the other 

 hand, we now know that bile pigments are more widely distributed 

 in nature than was previously assumed (cf. Chapter XI, 11.) and 

 that they also occur as products of plants {cf. Section 7 of this 

 chapter). 



1.2. Structure 



All the tetrapyrrane derivatives found in nature contain a skeleton 

 of four pyrrolic rings linked by three carbon atoms, a structure 



Fig. 1. Bile pigment skeleton. 



which is usually represented as a linear chain with an cfxygen atom 

 at both ends (Fig. 1 — on stereochemical grounds, this formula in most 



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