342 



ANIMAL METABOLISM 



* Can be replaced by D-isomer. 



t Can be replaced by corresponding alpha-keto or alpha-hydroxy acid. 



Amination. The process of oxidative deamination, which all the amino 

 acids undergo (p. 351), is reversible in the case of glutamic acid. This 

 reversibility makes possible the synthesis of glutamic acid from a-keto- 

 glutaric acid and ammonia, as follows: 



COOH 



I 

 CO 



I 



CHs + NH3 



CH2 

 I 

 COOH 



a-Ketoglutaric acid 



- H2O 



(35) *" 

 ^+H20 



COOH 



■ 



"I 

 C=NH 



I 

 CH2 



I 

 CH2 



+ 2(H ) 

 (36)*' 



COOH 



I 

 NH.CH 



I 

 CH2 



- 2(H) I 



. (L-Glutamic acid ^^2 



COOH dehydrogenase) ^^^^ 



a-Iminoglutaric acid 



L-Glutamic acid 



This process takes place mainly in the liver and kidneys. 



The necessary hydrogen is obtained from the reduced forms of either 

 DPN or TPN, which of course are always available in the body as a 

 result of fat and carbohydrate metabolism. Since the a-ketoglutaric 

 acid is produced from carbohydrates, this process constitutes a link 

 between the metabolism of proteins and sugars. 



The ammonia must be provided from some dietary source, which 

 normally comes from the deamination of other amino acids. This means 

 that the above process, which may be called amination, does not result 

 in a net increase in the total supply of amino acids. Its value lies, rather, 



