CARBOHYDRATE METABOLIC PATHWAYS 



71 



to the acetoacetate produced (acetoacetate is generally 

 recognized as a by-product of fatty acid oxidation in the 

 liver). Moreover, it may be seen that all of the oxidized 

 fatty acid follows this route. The mechanism of fatty acid 

 oxidation is depicted in Fig. 3.4, and it will be observed 

 that there is continuing production of a two-carbon moiety 

 (acetyl CoA) which, as discussed above, is burned completely 

 to CO2, H2O, and energy via the Krebs cycle. All of the 

 enzymes connected with this ^-oxidation of fatty acids are 

 in the mitochondria, and although a few examples may be 

 found throughout the literature of extramitochondrial oxi- 

 dation of fatty acids, e.g., in peanut microsomes (9), the great 

 bulk of fatty acid oxidation appears to be of mitochondrial 

 origin. The oxidation of the second major class of food- 

 stuffs, viz., fats, thus appears to fall into line with carbo- 



Fig. 3.4. Mechanism of fatty acid oxidation: the fatty acid spiral. 

 Example: octanoic acid. 



