252 Charles Heidelberger and Van R. Potter 



optical purity of its precursor were subjected to enzymatic 

 conversion into a-ketoglutarate as illustrated in Fig. 9. The 

 success of this experiment adds further support to the stereo- 

 chemical interpretation of this phenomenon. Recently 

 Martins and Schorre (1950) have reported experiments, 

 similar to these in scope and results, with the use of deuterated 

 citric acids. 



85^' 



r 1 



2| 2 Chemically Prepared 



Fig. 9. Distribution of label in citrate and a-ketoglutarate 



from chemically prepared asymmetric citric acid (Wilcox, 



Heidelberger and Potter, 1950). 



On the basis of the experiments with isotopic CO2 and 

 oxaloacetate it would be predicted that citric acid derived 

 from labelled acetate or pyruvate should be asymmetrically 

 labelled, and that the ^*C should be located in the primary 

 carboxyl group other than the one labelled by COg. Further- 

 more, if any recycling should occur one would anticipate 

 a balance between the radioactivity of the "a" and the 

 tertiary carboxyl group. That such is the case was strongly 



