INTRODUCTION AND NOMENCLATURE 455 



biliverdin; since their structure is not yet established in every detail, 

 no systematic nomenclature can be applied. 



Lemberg restricted the use of the prefix "v'erdo" expressly to this 

 type of compound. Unfortunately, it was extended by other authors, 

 particularly the Heubner school * {1527) to cover a variety of green 

 compounds which are formed from hemoglobin under conditions 

 similar to those under which verdohemochrome arises from 

 hemochrome. 



This group of irreversibly altered green hemoglobins comprises a 

 variety of substances, such as sulfhemoglobin, the "choleglobin" of 

 Lemberg, the "pseudohfemoglobin" of Barkan, the "cruoralbin" of 

 Holden, and other similar substances. While the spectroscopic prop- 

 erties (not, however, other properties) of these substances resemble 

 each other, they are quite distinct from those of verdohemochromes. 

 This dissimilarity persists if the pigments obtained from hemoglobin 

 are converted to hemochromes, or if verdoheme is combined with 

 globin. The verdohemochromes have their main absorption band 

 at 660-640 m^, the hemochromes derived from green hemoglobins at 

 630-610 TajjL, with the exception of sulfhemoglobin which is recon- 

 vertible to protohemochrome. The use of the same name to cover all 

 these substances is, therefore, misleading and should be avoided. 

 Until we know more about their structure they are adequately 

 described as green hemoglobins or hemochromes. 



Again, Barkan on the basis of assumptions which were later known 

 to be partly erroneous classified all the pigments under the terms 

 pseudohemoglobin and pseudohemochromogen. 



While the structure of verdoheme is estabhshed except for minor 

 details, that of the other compounds is still unknown. It has become 

 increasingly clear that they differ in their constitution more from 

 each other than their spectroscopic similarity would suggest. None 

 of the names in use, including our name "choleglobin," is very satis- 

 factory, but at the present stage it appears to be best to describe 

 them by the name given to them by the various authors who first 

 obtained them by a particular procedure. They have been sum- 

 marized in Table I. It must be left to further research to establish 

 their constitution and the greater or lesser degree of structural 

 similarity between them. At present one can only say with certainty 



* Kiese and Kaeske (1527) state that in adopting this nomenclature Heubner 

 followed the example of Lemberg. This is in error; compare also {622). 



