48 



David Shemin and Jonathan Wittenberg 



C2, D2, the alpha carbon atom of the pyrrole ring on the 

 side of the vinyl and propionic acid side chains, were derived 

 from the a-carbon atoms of glycine (Fig. 3). The findings 

 that the activities of Rings A and B is equal to that of Rings 

 C and D and that the carbon atoms in the pyrrole rings derived 

 from glycine are in comparable positions (underneath the 

 longer side chains) supports the earlier suggestion of a 

 common precursor pyrrole. 



In this degradation we have isolated, as mentioned above, 

 only thirty of the thirty-four carbon atoms of the porphyrin, 



CH, 



CH3 CH, 

 CH, 



COOH 



CH- 



CHp 



II ^ 

 CH 



B 



■rt 



^ 



N 



CH^ 



// 



CHp CH- 



CHg 



COOH 



PROTOPORPHYRIN 9 



CHgNHgCOOH 



Fig. 3. Positions in protoporphyrin derived from the rx-carbon 



atom of gly cine. 



and of these thirty carbon atoms four (carbon atoms numbered 

 2) are derived from the a-carbon atom of glycine. It can now 

 be easily demonstrated that the four methene bridge carbon 

 atoms are also derived from the a-carbon atom of glycine 

 (Muir and Neuberger, 1950; Wittenberg and Shemin, 1950). 

 The total activity of the porphyrin in this experiment was 

 5236 cpm (Table II). However, the sum of the total activities 

 of methylethylmaleimide and hsematinic acid, representing 



