CHAPTER VI 



HEMOGLOBIN 



1. INTRODUCTION 



1.1. Definition of Hemoglobin 



In the previous chapter we have seen that heme combines with 

 various nitrogenous compounds to form hemochromes. Toward car- 

 bon monoxide and oxygen the hemochromes behave as does heme; 

 both are able to form dissociable compounds with carbon monoxide 

 while reaction with oxygen leads to rapid oxidation to ferric com- 

 pounds. 



When heme is combined with the protein globin, the resulting 

 substance, hemoglobin, is able to form a dissociable compound with 

 oxygen in which the iron remains in the ferrous state. If the environ- 

 ment of the hemoglobin molecule is otherwise held constant, the 

 fraction combined with oxygen is found to be a function of the 

 partial pressure of the gas. On evacuation, molecular oxygen is set 

 free. This unique property distinguishes hemoglobin from other 

 classes of hematin compounds. 



This behavior is based on the electronic configuration of the iron 

 atom within the compound. Metalloporphyrins in which the iron is 

 replaced by another element, are able to combine with globins {1282, 

 1313), but such metalloporphyrin globin compounds have not been 

 reported as being able to unite reversibly with oxygen. The por- 

 phyrin nucleus and the globin are, however, also important, since no 

 ferroporphyrin compounds with proteins other than globin, nor any 

 other type of iron compounds are known which possess this property. 



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