CHAPTER VI 



THE ROLE OF ACETIC ACID, FORMIC 



ACID, AND PROPIONIC ACID IN THE 



INTERMEDIARY METABOLISM OF FATS 



The metabolism of acetic and formic acids plays a commanding role in 

 the intermediary metabolism of fats and of other foodstuffs. It would 

 appear to be more appropriate to consider the metaboUsm of these fatty 

 acids apart from the general discussion of fatty acid metabolism rather 

 than to attempt to correlate this information \\'ith the general pattern of 

 synthesis and oxidation of fat. 



1. Acetic Acid and Acetate 



Acetic acid plays a key role in the metabolic processes of the animal 

 body. On the one hand, it serves as the main building stone in the sjti- 

 thesis of long-chain fatty acids. On the other hand, it is the fragment 

 which is broken off from the fatty acid chain by /3-oxidation. In the 

 presence of carbohydrate, the acetate, so formed, combines with oxalo- 

 acetate to become incorporated into the tricarboxylic acid cycle, to com- 

 plete the oxidation of the fatty acid to CO2 and H2O. In the absence of 

 carbohydrate, two acetate molecules combine to form the ketone bodies. 



In addition to these all-important functions in the synthesis and oxidation 

 of fatty acids, acetic acid is known to be built up into the steroid nucleus 

 (see Chapter VIII). Another important function, which it serves, is that 

 of acetylation, whereby it reduces the toxicity and physiologic activity of 

 the amines. It may also function in the synthesis of porphyrin and uric 

 acid, while it can form glucose to a limited extent. There is considerable 

 evidence to suggest that, in all these reactions, acetic acid is present in a 

 biologically active form, which has been identified as acetyl CoA (see 

 Chapter II). Bloch^ has written a comprehensive review of all phases of 

 the metabohsm of acetic acid. 



' K. Bloch, Physiol. Revs., 27, 574-620 (1947). 



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