FAT -^ CARBOHYDRATE CONVERSION 233 



however, one must realize that these fats are artificial, and are not found as 

 natural products. 



The most probable explanation for the appearance of the small amounts of 

 fatty acid carbon in the carbohydrate' nioiocule is as follows. Under normal 

 conditions, the acetic acid molecules arising from the oxidation of the fatty 

 acids are combined with oxaloacetate, and they are oxidized via the Krebs 

 cycle. When the oxidation is complete, the new oxaloacetate may carry 

 one of the carbons from the original acetic acid. The oxaloacetate is readily 

 converted to pyruvic acid by decarboxylation. The resulting pyruvic acid, 

 still carrying the fatty acid carbon, is in equilibrium with glycogen. How- 

 ever, this reaction is a minor one; it simply means that some of the gly- 

 cogen carbon is replaced by fatty acid carbon. The total amount of glyco- 

 gen available remains constant. 



