PORPHYRINS 



found that the formaldehyde hberated upon periodate oxidation 

 of a crude fraction containing 5-aminolevuhnic acid was highly 

 radioactive. 



It now remained to establish more directly the utilization of 

 5-aminolevulinic acid for porphyrin formation. The compound 

 was synthesized with C^'* in its 5-carbon atom, and its utilization 

 was compared with that of glycine. It can be seen from 

 Table II that the hemin synthesized from an equimolar amount 



TABLE II 



Comparison of C'^ Activities of Hemin Samples 



Synthesized from Glycine-2-C^^ (0.05 mc./mM) 



AND 5-Aminolevulinic Acid (0.05 mc./mM) (28,29) 



C'^ Substrate 



Other Additions 



Activity 



of Hemin 



(c.p.m.) 



Glycine-2-C (0.05 mM) 

 5-AminolevuIinic acid (0.05 mM) 

 S- Aminolevulinic acid (0.05 mM) 



Succinate (0.1 mM) 



Glycine (0.33 mM) 

 Succinate (0.1 mM) 



333 

 23,000 

 21,000 



of 5-aminolevulinic acid was about 65 times more radioactive 

 than hemin synthesized from glycine. More rigorous proof 

 that 5-aminolevulinic acid is indeed the precursor for porphyrin 

 synthesis was obtained by degrading a hemin sample synthesized 

 from 5-aminolevulinic acid-5-C^^ and from 5-aminolevulinic acid- 

 1,4-C^^. The 5-carbon atom of the former compound should 

 label the same carbon atoms of protoporphyrin as those which 

 we have previously found to arise from the a-carbon atom of 

 glycine, since according to the hypothesis the latter carbon 

 atom is the biological source of the 5-carbon atom of 5-amino- 

 levulinic acid. Furthermore, the 5-aminolevulinic acid-l,4-G^^ 

 should label the same carbon atoms of protoporphyrin found to 

 arise from the carboxyl groups of succinate, since from Figures 

 1 and 4 these carbon atoms arise from succinate. 



It can be seen from Table III that the same C^^ distribution 

 pattern was found in protoporphyrin synthesized from 5- 



527 



