62 



David Shemin and Jonathan Wittenberg 



COOH 



CHp 



CH2-- 



CHo 

 I ^ 



CH2 

 ■COX 



COOH of the succinyl derivative may then 



condense with glycine to form a pyr- 

 role containing a carboxymethyl and 

 a carboxyethyl group in its ^-positions 

 (see Fig. 7). 



The formation of protoporphyrin 

 may therefore be visualized as follows 

 (Fig. 8). Four of these mono-pyrroles 

 are condensed, with the loss of the 

 a-carboxyl group of the pyrrole and 

 with the addition of a compound 

 originating from the a-carbon atom of 

 glycine, by a mechanism outlined in a 

 previous paper (Wittenberg and Shemin, 1950), where it was 

 suggested that the compound may be combined with a co- 

 enzyme and be utilized in a manner analogous to the synthesis 

 of porphyrins described by Andrews, Corwin and Sharp 

 (1950). The tetra-pyrrole first formed would be uroporphyrin 

 III, which by decarboxylation of the carboxymethyl side 



CPX CH2-COOH 

 H2N 



Fig. 7. Hypothetical 

 scheme for formation of 

 common precursor pjTrole 

 from glycine and the suc- 

 cinyl derivative. 



COOH 

 COOH CH2 

 CH2 CH2 



H^ N^COOH 

 H 



1 



COOH 

 CHj 

 CH3 CH2 



^ UROPORPHYRIN 



■^ COPROPORPHYRIN 



PROTOPORPHYRIN 



H N XOOH 

 H 

 Fig. 8. Hypothetical scheme for formation of protoporphjTin 

 from common precursor pyrrole. 



