DAVID SHEMIN 



N^^. It can be seen that whereas the incorporation of C'^ from 

 the glycine was lowered, there was a comparatively large in- 

 corporation of N^^ into the porphyrin, thus demonstrating that 

 the lowered C^^ activity of the hemin sample was due to dilution 

 rather than inhibition. Further proof that 5-aminolevulinic 

 acid arises by the condensation of glycine and succinate was 

 obtained by incubating red blood cell hemolyzates with glycine- 

 2-C^^ and unlabeled 6-aminolevulinic acid, and subsequently 

 isolating the 5-carbon atom. In such an experiment it was 



TABLE I 



Comparison of G"-Activities of Hemin Samples Synthesized from 



Glycine-2-C" (0.05 mc./mM) or Succinic Acid-2-Ci* (0.05 mc./mM) in 



THE Presence and Absence of Nonradioactive 5-Aminolevulinic Acid (28,29) 



" The isotopic concentrations of these samples were 34 atom % excess Ni*. 

 In each of the experiments the volume of the hemolyzed preparation was 30 ml. 

 Unlabeled succinate (0.1 mM) was added to the flasks in which labeled glycine 

 was the substrate, and unlabeled glycine (0.33 mM) was added to the flasks in 

 which labeled succinate was the substrate. Each flask contained 1 mg. of iron 

 (ferric). 



526 



