Biosynthesis of Porphyrins 



47 



that from the a-ketobutyric acid hydrazone samples repre- 

 sented carbon atoms A2, B2 and C2, D2. The acetic and 

 propionic acid samples were then degraded stepwise by 

 repeated Schmidt reactions on the free acids, liberating carbon 

 dioxide from positions shown in Fig. 2. In this degradation 

 scheme, not only can the ^*C activities of the individual 

 carbon atoms be determined, but their ^*C activities can be 

 checked by comparing the sum of the activities of the 

 individual carbon atoms to that of the parent compound from 

 which they are derived; e.g. the sum of the individual activi- 

 ties of carbon atoms numbered 6, 4 and 5 can be compared 

 to the activity of the pyruvic acid and likewise the sum of 

 the activities of the keto acids can be compared to the activity 

 of the maleimide samples. 



These degradation procedures were then utilized for the 

 determination of the position in the porphyrin molecule of the 

 carbon atoms which were derived from the a-carbon atom 

 of glycine. Duck blood was incubated with glycine labelled 

 with ^*C in its a-position and the hsemin isolated and degraded 

 (Wittenberg and Shemin, 1950). It was found that the 

 fraction representing Rings A and B (methylethylmaleimide) 

 had the same activity as the fraction representing Rings C 

 and D (Table II). Further degradation showed that all the 

 activity of these fractions was contained in the a-ketobutyric 

 acid. On degradation of the latter all the activity was found 

 in the carboxyl group. Therefore carbon atoms A2, B2 and 



Table II 



Distribution of ^^C Activity in Protoporphyrin Synthesized from i*C 

 Methylene Labelled Glycine,^ (NHa^^CHg-COOH) 



(Wittenberg and Shemin, 1950) 



