258 VI. ACETIC. FORMIC, AND PROPIONIC ACIDS 



Their data, likewise, indicated that the change, palmitic acid -*■ myristic 

 acid, occurs in tissues.^ In both of these reactions, a two-carbon fragment 

 is broken off. Likewise, Weinhouse and collaborators,^'' who investigated 

 the oxidation of carboxyl-labeled octanoic acid, demonstrated that the 

 acetoacetate formed contained C^^ in both the carboxyl and the carbonyl 

 group; these data could only be interpreted as indicating that the aceto- 

 acetate had originated by random conjugation of two C2 fragments which 

 had been the primary degradation products. 



A more direct proof of the origin of acetic acid in fatty acid oxidation 

 has been obtained by the use of the acetylation reaction. Since the acetyl 

 group, CHs-CO, is readily derived from acetic acid, its presence affords 

 an excellent criterion as to the availability of the acetate molecule. Bloch 

 and Rittenberg^^ demonstrated that, when deuteriobutyric acid, deuterio- 

 ??-valeric acid, alanine, and deuteriomyristic acid were fed, deuterioacetyl 

 groups were present in the acetylated amines. On the other hand, tagged 

 propionic acid and undecylic acids failed to yield acetyl groups. The 

 results were in harmony with the assumption that /3-oxidation occurs, and 

 that the acetyl groups originate on removal from the /3-keto acids. 



b. Formation from Odd-Chain Fatty Acids. The odd straight-chain 

 fatty acids are ordinarily not found in animal tissues, but they can be 

 oxidized as readily as the even-chain acids. In contradistinction to other 

 odd-chain acids with more than three carbons, propionic acid cannot form 

 ketone bodies; it is also a source of glycogen, and it exhibits other properties 

 in harmony with this behavior. Bloch and Rittenberg^^ likewise support 

 this viewpoint, smce propionic acid was shown to be incapable of yielding 

 acetyl groups for the acetylation of phenylaminobutyric acid. This 

 latter fact also indicates that propionic acid is not metabolized via pyruvic 

 acid, inasmuch as the keto acid was found to be a potent source of the 

 acetyl radicle. 



The experiments with w-valeric acid (CHs-CHa-CHa-CHa-COOH), 

 in which the acid was tagged with deuterium, indicate that the acid gives 

 rise to acetic acid to the extent of one molecule.*' The remaining three- 

 carbon fragment is the source of glucose.*^'** On the other hand, isovaleric 

 acid ((CH3)2:CH-CH2-COOH) was shown by Cohen,^^ by the use of liver 

 slices, to be a much more potent source of acetate than was its normal 



M S. Weinhouse, G. Medes, and N. F. Floyd, /. Biol. Chem., 155, 143-151 (1944). 



31 K. Bloch and D. Rittenberg, J. Biol. Chem., 155, 243-254 (1944). 



'2 J. S. Butts, H. Blunden, W. Goodwin, and H. J. Deuel, Jr., /. Biol. Chem., 117, 

 131-133 (1937). 



33 H. J. Deuel, Jr., J. S. Butts, L. F. Hallman, and C. H. Cutler, /. Biol. Chem., 112, 

 15-23(1935-1936). 



