396 LECTURE XVII. 



the system in an inorganic form can take part in the formation of 

 hemoglobin. The question then naturally arises, Have the proper means 

 been found for solving this problem ? Up to this point, in discussing the 

 formation of hemoglobin, we have considered but one component of hema- 

 tin; namely, the iron. It seems hardly justifiable to limit the entire dis- 

 cussion to this one component. We know that the chemical composition 

 of hematin is very complicated. 1 M. Nencki and J. Zaleski 2 have sug- 

 gested the following structural formula for hemin, the hydrochloric acid 

 ester of hematin: 



CH 2 CH 2 



CH (OH)C/\ CH 



i 



rt lpTT 



,\/C\/ CH 

 |CH 2 NH 

 



CH 2 



(OH)C 



CH 2 HN 



We introduce this formula here merely to show how complicated its 

 synthesis must be if the animal cells are to build it from inorganic iron. 

 The formula also shows that obviously the iron itself does not play such 

 an all-important part in the synthesis; that is to say, it is probably not so 

 very difficult to introduce the iron into the molecule. It is infinitely 

 more important to know whether the organism has other organic material 

 available for the formation of the hematin. 



In the above formula we see that two hematoporphyrin molecules 

 (the iron-free cleavage-products of hematin) are held together by an iron 

 atom. The formation of hematin, therefore, depends just as much upon 

 the presence of material from which hematoporphyrin can be made as upon 

 the presence of iron. Now we know, as will be explained subsequently 

 in detail, that hematophorphyrin is closely related to chlorophyll, 3 for 

 similar decomposition products are formed from each of these two com- 

 pounds. This suggests the thought that chlorophyll can perhaps be 

 brought into relation with hematin, and thus with the formation of hemo- 

 globin. There is absolutely no doubt that these compounds are closely 

 related to one another. The fact that both, as we shall see later on, 

 possess similar biological functions is sufficient to explain this relation- 

 ship, although, as a matter of fact, the task of chlorophyll is quite different, 

 as far as our knowledge goes, from that of hemoglobin. Now, inasmuch 



1 See Lecture XXIV. 



2 Ber. 34, 997 (1901). 



3 L. Marchlewski: Die Chemie des Chlorophylls (1895). 



