Asymmetric Citric Acid 255 



in the degradation by the homogenate has also been ehminated 

 because identical results were obtained when aliquots of the 

 same sample of citric acid were degraded by the homogenate 

 and pigeon liver extract, in which cycling is not possible. 

 Another plausible explanation, that of COg fixation, has also 

 been ruled out by an experiment with [car&oa??/-^*C] -pyruvate, 

 in which no ^^C could be detected in the citric acid. 



Two other possibilities are now under investigation. One 

 is that some succinate can break through the malonate block, 



HOOCCH CO + (-CH COX) *- CH 5oOH 



COOH 



Intact Rat (Kidney) 

 Fluoroacetate Poisoned 



HOOCCH^COHCH^COOH 

 2| 2 



COOH 



20^ 



EOOCCOCH2CE2COOH 



1 

 1 



Pigeon Liver Extract 



KMnOy^ 



CO^ + HOOCCH^CH^COOH 



80% 20% 



Fig. 12. Distribution of label in citrate and c -ketoglutarate 



from labelled acetate in the intact rat (Potter, Heidelberger 



and Busch, 1951, unpublished). 



be preferentially oxidized and cajry through to oxaloacetate 

 in an asymmetric fashion, possibly as phosphorylated inter- 

 mediates. The other hypothesis currently under investigation 

 is that oxaloacetate may exchange with acetate by the 

 splitting off of oxalic acid or a derivative. The results of these 

 experiments are not yet available. 



In conclusion, it may be seen that a study of the asymmetry 

 of labelled citric acid has substantiated Ogston's proposal, 



