CHAPTER XIII 



FORMATION OF HEMOGLOBIN 



AND SYNTHESIS OF PORPHYRINS 



IN THE ANIMAL BODY 



1. INTRODUCTION 



Little is known about the formation of the hematin enzymes or of 

 those hemoglobins (erythrocruorins) which are found circulating free 

 in the plasma of some invertebrates. The bulk of our knowledge of 

 the biochemistry and physiology of hematin synthesis is drawn from 

 studies on the formation of hemoglobin in higher animals, in which 

 hemoglobin is formed inside the erythrocytes. This introduces a 

 complication, since it is often difficult to decide whether a substance 

 with hemopoietic activity is required for the synthesis of hemo- 

 globin, be it as building stone or as catalyst of the synthetic process 

 ("hemopoiesis" in the narrower sense of the term), or for the building 

 up of the red cell architecture, the "stroma," and the formation of a 

 stable erj^throcyte ("erythrocytopoiesis" or "cytopoiesis"). In more 

 primitive organisms, however, it may be more difficult to separate 

 the synthesis of hematin compounds from general cell synthesis 

 than in the case of higher animals where considerable interference 

 with the processes of hemoglobin synthesis is possible without 

 endangering the life of the organism. 



2. SOME HEMATOLOGIC DATA 



Although it is beyond the scope of this book to give an introduction 

 to hematology, certain essential anatomic and histologic facts are 

 necessary for understanding the biochemistry of hemoglobin syn- 

 thesis in the animal body. 



60.S 



