72 



METABOLIC PATHWAYS IN MICROORGANISMS 



hydrate oxidation, so far as intracellular location of the en- 

 zymes is concerned. 



The oxidation of the third major class of foodstuffs, 

 namely the amino acids, is siuiimarized briefly in Fig. 3.5. 

 Here it will be seen that many of the common amino acids 

 are in equilibrium with specific compounds in the Krebs 

 cycle (pyruvate, a-ketoglutarate, or oxalacetate) and exten- 

 sive research has shown that for the most part the specific 

 amino acid dehydrogenases, as well as the transaminases 

 necessary to produce these key intermediates, are located in 

 the mitochondria. 



Alanine 



Valine 



Serine 



C4 



Threonine 

 Aspartic acid 



Glutamic acid 



Proline 



Hydroxyproline 



Arginine 



Histidine 



Lysine 



Serine 



^ 



Fig. 3.5. Protein degradation and tlic TCA c\cle. 



