TRANSAMINATION 



217 



The inability of purified transaminase preparations to dehydrogen- 

 ate glutamic or aspartic acids in the presence of suitable hydrogen 

 acceptors, and the absence of free ammonia during the course of 

 the reaction suggest that the amino group is transferred through 

 an intermediate complex of the SchiflF's base type. 



Karrer et al. (28) have investigated the metabolism of octopin, 

 following the suggestion of Knoop and Martins (29) that octopin 

 represents a naturally occurring intermediate compound of trans- 

 amination. Karrer et al. found that fresh Hver brei (which they 

 state contains an Z-amino acid dehydrogenase) was capable of de- 

 hydrogenating octopin. d-Amino acid dehydrogenase preparations 

 were not active, indicating that the alanine was of the Z-form. Since 

 the biological synthesis of octopin involves an intermediate reduc- 

 tion of a SchifiF's base to an a, a'-imino dicarboxylic acid, the authors 

 conclude that transamination may involve intermediate reduction of 

 the Schiffs base with subsequent dehydrogenation. The reaction is 

 pictured as follows: 



SCHEME II 



R R, 



I I 



H-C-NHp + 0=0 



I I 



COOH COOH 



-^^ H-C— N=C 



COOH COOH 



+ H; 



R 



H 



R, 



R R, 



I I 



C=0 + HpN-C-H 



I I 



COOH COOH 



H-C— N— C-H 



I I 



COOH COOH 



-Hz 



R R, 



+H2O I I 



^-^- C=N— CH 



I I 



COOH COOH 



It has the advantage of providing a mechanism for the explana- 

 tion of the double bond shift between the nitrogen and the two 

 alpha carbon atoms. 



As previously pointed out, the evidence for the existence of a 



