SYNTHESIS OF THE PORPHYRIN NUCLEUS 



643 



In the megaloblast — i.e., hemopoiesis of the embryo — and also 

 in porphyria, the decarboxylation of A is incomplete. In reaction 8 

 and 9, which correspond to reactions 2 and 3 of the decarboxylated 

 series, two dipyrrolic compounds are formed which yield the uropor- 

 phyrins I and III. The formation of uroporphyrin II is again excluded 

 by a,a'-disubstitution of one of the dipyrrolic compounds. Reaction 4 

 is admittedly an ad hoc assumption, but it allows a great simplifica- 

 tion of the scheme. 



-^^ ► proto IX ► hemoglobin 



Fig. 9. Relation between coproporphyrin I and III formation and hemopoiesis. 



8.2.2. Ratio of Type I to Type III Porphyrins. It is now of 



interest to investigate the consequences of this theory. By an approxi- 

 mative mathematical treatment one can predict that hemopoiesis 

 will influence the ratio of coproporphyrin I formation to that of the 

 III isomeride {cf. Fig. 9). 



Assume that a fraction x of fi is transformed to C and (1 — x) to D, that 

 of Z) a fraction y is used for the synthesis of protoporphyrin IX and hemo- 

 globin, while (1 — y) is used for the synthesis of coproporphyrin III; of C 

 a fraction z is used for synthesis of protoporphyrin IX and hemoglobin, a 

 fraction w for the synthesis of coproporphyrin I, leaving 1 — w — z for the 

 synthesis of coproporphyrin III. It is, assumecr that the other reactions 

 {e.g., E ^^protoporphyrin IX) proceed to 100%. Hence one molecule of D 

 reacts with one molecule of E derived from one molecule of C. From this 

 stoichiometry of the formation of protoporphyrin IX, it follows that: 



Dy = Cz 



or: B {I — x)y = Bxz 



X 



(1) 



