70 METABOLIC PATHWAYS IN MICROORGANISMS 



soluble enzymes had virtually no power to oxidize Krebs 

 cycle intermediates (succinoxidase activity), the mitochon- 

 dria by contrast showed a great ability to do so. In Table 

 3.2, Green et al. (7) have assembled all of the Krebs cycle 

 intermediates and have shown that kidney mitochondria 

 can oxidize these substrates completely, or, as shown in 

 the lower half of the table, can produce COo from these 

 oxidations in theoretical yields. If one assumes the pres- 

 ence of enzymes that will produce pyruvate from glucose in 

 an organism, it is clear that the oxidation of carbohydrates, 

 the first great class of foodstuffs, can be explained by the 

 activity of mitochondria; extramitochondrial Krebs cycle 

 oxidations are rare in most organisms. 



The mitochondria may be shown to be potent fatty acid 

 oxidizers also. As Table 3.3 shows, caproic acid is oxi- 

 dized by rabbit liver mitochondria, in amounts equivalent 



TABLE 3.3 



Oxidation of Caproic Acid to Acetoacetic Acid, Carbon 

 Dioxide, and Water in Rabbit Liver Mitochondria 



After Cheldehn et al. (8). 



