TRIGLYCERIDES AND FATTY ACIDS 87 



in the oxidation of short-chain fatty acids of the even series, namely CH3 • - 

 CO — and — CHoCO — . Two types of acetoacetate will be formed, one 

 by the condensation of the first with the second type of C2 compound, while 

 the second arises exclusively from the second type. It is believed that, 

 when acetoacetate is synthesized by slices or by washed homogenates of 

 rat liver, the activity of 40 to 50% of the terminal two-carbon groups is 

 identical with that of the two-carbon fragments from the rest of the mole- 

 cule. The occurrence of asymmetric labeling of acetoacetate is related to 

 the proportion of the two types of two-carbon compounds from which the 

 acetoacetate is derived. 



d. co-Oxidation Theory. In addition to oxidation on the ;S-carbon, the 

 fatty acids of medium chain length have been shown in some cases to be 

 first oxidized on the w- carbon, i.e., on the terminal carbon furthest from the 

 carboxyl group. As a result of this type of oxidation, dicarboxylic acids 

 are produced which apparently are then broken down by /3-oxidation, 

 from either or both ends. Verkade, van der Lee et a^^^'^^ were the first 

 investigators to recognize this type of oxidation. It was demonstrated 

 that, in man, the ingestion of glycerides of capric acid and of undecanoic 

 acid was followed by the excretion of dicarboxylic acids. Nonanoic acid®^ 

 and caprylic acid had weak diacidogenic properties; lauric acid glycerides 

 gave rise only to traces of dicarboxylic acids or to none at all, while tri- 

 decanoic acid was devoid of diacidogenic effects.^^ In the case of the dog, 

 the metabolic pattern for the C7 to Cn acids differed somewhat. Accord- 

 ing to Verkade,®^ this discrepancy may be related to the fact that, in contra- 

 distinction to man, it is difficult to produce ketosis in the dog, and that the 

 lack of diacidogenesis is "possibly related and to be expected with the 

 carnivora in general." 



It has been observed that co-oxidation does not occur in the case of straight- 

 chain fatty acids having more than twelve carbon atoms. In contra- 

 distinction to this finding is the demonstration by Weitzel^^ of this type of 

 oxidation, as evidenced by the presence of dicarboxylic acids in the urine of 

 dogs after the feeding of a-substituted myristic or stearic acid in which the 

 side chain has more than one carbon. As far as is known, this is the only 

 example of co-oxidation of C14 or C18 fatty acids. 



The possible course of oxidation of the terminal methyl group which 



" P. E. Verkade and J. van der Lee, Biochem. J., 28, 31-40 (1934). 



*^ P. E. Verkade, M. Elzas, J. van der Lee, H. H. de Wolff, A. Verkade-Sandbergen, 

 and D. Van der Sande, Proc. Acad. Sci. Amsterdam, Sect. Set., 35, 251-266 (1932); 

 P. E. Verkade and J. van der Lee, Ihid., 36, 314-323 (1933). 



«« P. E. Verkade, Chemistry & Industry, 57, 704-711 (1938). 



" G. Weitzel, Z. physiol. Chem., 287, 254-296 (1951). 



