The Biosynthesis of Porphyrins 



2m 



of decarboxylation would be 8-aminolevulinic acid, and condensation 

 of two moles of the latter compound, by a Knorr type of condensation 

 (Fig. 8) would give a reasonable mechanism for formation of a pyrrole 

 in which the a-carbon atom of glycine would be distributed in the 

 positions previously observed. To test this hypothesis, S-aminolev- 

 ulinic acid was synthesized and its utilization for porphyrin synthesis 

 studied. 16 - 18 



In the initial experiments, unlabeled 8- aminolevulinic acid was added 

 to duck red blood cell hemolyzates along with either C 14 -labeled glycine 

 or C 14 -labeled succinate. The radioactivities of the hemin samples iso- 

 lated in these experiments were compared with those obtained from 

 controls in which the unlabeled 8-aminolevulinic acid was omitted. The 

 rationale for these dilution-type experiments is as follows: if 8-amino- 

 levulinic acid is an intermediate formed from the condensation of 

 glycine and succinate, any labeled 8-aminolevulinic acid formed 

 from these labeled substrates will be diluted by the added unlabeled 

 compound, and consequently this should be reflected in the lowered 

 radioactivity of the hemin samples synthesized in the presence of un- 

 labeled 8-aminolevulinic acid. It can be seen from Table 2 that the 

 hemin samples made in the presence of unlabeled 8-aminolevulinic acid 



Table 2. Comparison of C 14 Activities of Hemin Samples Synthesized 

 from Glycine-2-C 14 (0.05 mc./mM) or Succinic Aeid-2-C 14 (0.05 mc./mM) 

 in the Presence and Absence of Non-radioactive 6-Aminolevulinic Acid 



* The isotopic concentrations of these samples were 34 atom % excess N'°. 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 m°. of iron (ferric). 



