308 VII. COMPARATIVE BIOCHEMISTRY OF HEMOGLOBINS 



hemoglobin" rather than erythrocruorin. At the present time, however, 

 the nomenclature of the oxygen carriers is becoming increasingly complicated 

 from the point of view of phylogenetic origin; Virtanen and Laine {2891) 

 suggest the term "leghemoglobin" for the root nodule pigment. There are 

 in addition, certain chemical reasons which reinforce the desirability of 

 revising the phylogenetic nomenclature. Pending such a revision, we shall 

 use the term erythrocruorin. Where we discuss the ferric derivatives of 

 these pigments, we use the term ferrierythrocruorin for metaerythrocruorin, 

 the ferric form of the native pigment {cf. Chapter VI). 



3. CHEMICAL BASIS OF SPECTROSCOPIC 

 DIFFERENCES 



3.1. Classification 



The diversity of hemoglobins in the animal kingdom was brought 

 to light by spectroscopic methods. The spectrum depends on the 

 derivative examined, on the structure of the prosthetic group, on 

 the influence exerted by the protein, and perhaps on environmental 

 factors. The influence of the different prosthetic groups is far greater 

 than the influence of a different protein. If two pigments carry the 

 same prosthetic group, the spectroscopic differences between them 

 are almost abolished when the protein is denatured. A differentiation 

 into green and red oxygen carriers, based on the prosthetic group, 

 was soon recognized. The former class comprises the chlorocruorins, 

 the latter, the erythrocruorins and hemoglobins. The variations 

 between the spectra of chlorocruoriu from different species and 

 between the spectra of the different members of the class of erythro- 

 cruorins and hemoglobins are not greater than would be expected 

 from variations in the protein. 



3.2. Chlorocruorin 



Although the character of the spectrum of this compound is quite 

 different from that of hemoglobin, the changes observed when differ- 

 ent derivatives are formed, are familiar. It is capable of reversible 

 oxygenation, it can form a ferrichlorocruorin (metachlorocruorin) and 

 it forms hemochromes which can readily be distinguished from those 

 containing protohematin. Table II summarizes Fox's observations 

 {931) on the spectroscopy of chlorocruorin, the band position being 

 measured with a Zeiss microspectroscope and in the case of oxychloro- 

 cruorin and ferrochlorocruorin, by spectrophotometry. 



The porphyrin of the prosthetic group of chlorocruorin is called 



