224 



A SYMPOSIUM ON RESPIRATORY ENZYMES 



represent a single enzyme system, as is the case with ci-amino acid 

 dehydrogenase. 



The mechanism of deamination of Z-amino acids in Hver and 

 kidney can be explained on the basis of the above theory. However, 

 the failure of the other tissues to oxidize amino acids other than 

 glutamic acid to any appreciable extent is difficult to explain, since, 

 as was said above, the two necessary enzyme systems are present in 

 most tissues. Inasmuch as the theory rests in large measure on 

 Braunstein's claim that all amino acids are active in transamination, 

 unequivocal proof for this would seem desirable. As previously 

 pointed out, experiments by the writer have shown transamination 

 to be a limited reaction rather than a general one. Further, the 

 author has found that homogenized liver and kidney, fortified with 

 cozymase and methylene blue, failed to show any appreciable 

 yields of ammonia from various combinations of alpha-ketoglutaric 

 acid and Z- amino acids (63). 



A possible metabolic relationship between transamination and 

 protein synthesis in animal tissues has been pointed out by Linder- 

 str0m-Lang (52). On the basis of the plausible assumption that the 

 synthesis of protein occurs by a metabolic mechanism other than 

 the reversal of proteolysis, he postulates the following scheme: 



OH 



SCHEME III 



-H2O 



R-C-C-OH + HpNR, 



I 

 H 



O OH 



li I 

 ^ R-C-C-N-R, 



I I 

 H H 



-H2 

 O OH 



NHp O H 

 \^ II I 

 R-C-C-N-R, 



I 

 H 



+ 



R-C-C=N-R, 



.Glutamic 

 , Acid 

 NH2 OH 



I / 



R-C-C=N-R, 



H 



ex Ketoglutaric 

 Acid 



