PORPHYRINS 



hemolyzed red blood cells (14,24) of a duck with the C^**- 

 labeled compounds, and subsequently chemically degrading the 

 isolated hemin. The degradation was done in such a manner 

 that individual carbon atoms from a particular position in the 

 porphyrin could be isolated (30,34). The carbon atoms arising 

 from succinate and glycine are shown in Figures 2 and 4. It 

 would appear merely from the C^^-labeling pattern obtained 

 that each pyrrole unit is made up of 2 moles of succinate and 1 

 mole of glycine. Since the methene bridges also arise from the 

 a:-carbon atom of glycine, the synthesis of the porphyrin mole- 

 cule requires 8 moles of both succinate and glycine. 



It then became of interest to find the chemical mechanism 

 by which the succinate and glycine combine to form the pyrrole 

 unit of the porphyrin. Our studies on the utilization of the 

 a-carbon of glycine for porphyrin formation have led us to the 

 following mechanism. It was difficult for some time to under- 

 stand the distribution of the a-carbon atom of glycine in the 

 porphyrin molecule (four in the pyrrole rings and the four 

 methene bridge carbon atoms, Figure 2). A possible explana- 

 tion for the observed distribution of the a-carbon atom of 

 glycine was that the glycine was utilized for porphyrin synthesis 

 via two pathways. 



"x" ^ Pyrrole ring carbon atom 



/ 

 Glycine^ 



\ 



"y" > Methene bridge carbon atom 



Since the metabolic pattern of the a-carbon atom of glycine 

 was similar to that of the "Ci" compounds, and since the methene 

 bridge carbon atoms are no longer attached to the nitrogen 

 atom, it would appear that a "Ci" compound might be sub- 

 stituted for compound "y." Studies were undertaken to test 

 this point. In no case could CH3OH, HoCO, HCOOH, 

 CH3NH2, CO2, or CHO— COOH substitute for glycine. These 

 negative findings, coupled with the finding that the a-carbon 

 atom of glycine was always equally utilized for both the pyrrole- 



523 



