76 



A. Neuberger 



that formation of protein in the developing red cell precedes 

 that of porphyrin. This protein may, at such an early stage, 

 still be metabolically active, exchanging with the glycine 

 stores of the body, or it may not even be globin. But it is 

 possible that some of the reactions utilizing the methylene 



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HOURS 



14 



22 



DAYS 



52 



Fig. 4. Comparison of radioactivities of porphyrin, globin 

 glycine and stromatin glycine from rat erji:hrocytes obtained at 

 various times after simultaneous administration of the two 

 labelled amino-acids. Broken line refers to results obtained from 

 a rabbit. The porphjTin activities have been divided by eight. 



carbon atom of glycine for the synthesis of porphyrin are 

 slower than the incorporation of glycine into globin and thus 

 the isotope would appear at a later time in at least some of the 

 eight positions of the porphyrin. Experiments to test this 

 possibility are in progress. 



