SYNTHESIS OF THE PORPHYRIN NUCLEUS 645 



a specific role in increasing reaction 3, for which a monocarbon com- 

 pound is needed, and decreasing reaction 2 correspondingly. We 

 have seen that a decrease of x from 0.5003 to 0.50 eliminates copro- 

 porphyrin I formation. With the possible exception of the last- 

 mentioned case no alteration of the fraction x need be assumed in 

 order to explain variations in the ratio of the two coproporphyrins. 

 It is clear that a derangement of hemopoiesis can explain an increased 

 excretion of coproporphyrin III, (juite as well as an increased hemo- 

 poiesis explains that of coproporphyrin I. There is thus no necessity 

 to assume that coproporphyrin III is derived from hemoglobin 

 breakdown. 



The assumptions made hitherto on porphyrin formation have been 

 too simple, and did not take into account these complicated relation- 

 ships to hemopoiesis. The fact that the ratio of the coproporphyrin 

 isomerides in various pathologic conditions can be correctly predicted 

 by the present theory is strong evidence that it represents a step 

 forward. 



