244 



Essays in Biochemistry 



positions located are the four methene bridges 8,9 and one in each 

 pyrrole 8 (Fig. 3). It will be noticed that the carbon atoms in the 

 pyrrole rings, derived from the a-carbon atom of glycine, are in the 

 a-position under the vinyl and propionic acid side chains. This finding 

 supported the suggestion of a common precursor pyrrole first being 

 formed and led to the suggestion that the vinyl side chains arose from 

 propionic acid side chains by decarboxylation and dehydrogenation. 



CH, 



CH, 



II " 

 CH 



HC*<5 



CH, 



CH., 

 I " 

 CH, 

 I ' 

 COOH 



H 

 :C*- 



a 



7 

 :C*- 

 H 



CH 



CH, 



I " 

 CH, 



I " 

 COOH 



CH, 

 II 

 CH 



C'H/3 



CH : 



NH,-C'H,-COOH 

 Glycine -2 -C 14 



NH, - C*H, - CO - CH, - CH, - COOH 

 8 - Aminolevulinic Acid - 5 - C ' ' 



Protoporphyrin IX 



Fig. 3. The carbon atoms of protoporphyrin which arise from the a-carbon atom 

 of glycine and from the 5-carbon atom of 5-aminolevulinic acid. 



Having accounted for eight carbon atoms of protoporphyrin, the 

 origin of the remaining twenty-six carbon atoms remained to be deter- 

 mined. It had been found by Bloch and Rittenberg 13 that, on admin- 

 istration of deuterioacetic acid (CD 3 COOH) to a rat, the hemin 

 isolated contained deuterium. This indicated that some of the side- 

 chain carbon atoms, at least, were derived from the methyl group of 

 acetate, since these are the only carbon atoms bonded to hydrogen. 



In order to determine the extent of utilization of acetate for por- 

 phyrin synthesis and to locate all the carbon atoms which may be 

 derived from acetate, duck blood was incubated separately with C 14 - 

 methyl-labeled acetate and with C 14 -carboxyl-labeled acetate and the 

 resulting C 14 -labeled-hemin samples degraded by the method men- 

 tioned above. It was found that all the remaining twenty-six carbon 

 atoms were derived from acetate. 12 



The composite C 14 -distribution pattern among all the labeled twenty- 

 six carbon atoms derived from acetate is given in Fig. 4. Since all four 



