316 VII. COMPARATIVE BIOCHEMISTRY OF HEMOGLOBINS 



factory explanation for the isoelectric points in the neighborhood of 

 pK 4.5 to 5.3 found for these pigments. No data comparable to the 

 acid-base titration figures obtained by Cohn and co-workers i4-6S) 

 for carboxyhemoglobin are available for the invertebrate pigments. 



5.2.2. Vertebrate Oxygen Carriers. Recent work on the amino 

 acid composition of the hemoglobins has been stimulated by the 

 various theories of protein structure and by interest in the compara- 

 tive biochemistry of the proteins. We are primarily interested here 

 in the dependence of the reaction of hemoglobins on their amino 

 acid content and in the essential nutritional character of certain 

 amino acids for globin synthesis in some species. Most of the work 



TABLE VII 

 Amino Acid Content of Vertebrate Oxygen Carriers 



" Abbreviations are: r = rabbit, g = guinea pig, p = pig," d = dog, s = sheep, o = ox, 

 and m == human. 



on the latter has been carried out with species (e.g., rat and dog) 

 whose hemoglobins have not received much attention. 



