TRANSAMINATION 223 



present under way by the writer to determine the influence of other 

 vitamin deficiencies on this reaction. 



Role of Transamination in Intermediary Metabolism 



The exact role which transamination plays in intermediary metabo- 

 lism is still not clear. The substrates of this reaction are highly 

 reactive and participate in many diflFerent rapid metabolic proc- 

 esses. Obviously if transamination is to play a significant role in 

 cellular metabolism it must be shown to proceed at a rate rapid 

 enough to be quantitatively significant. From Table 1 it is apparent 

 that truly rapid rates are seen only with the system glutamic acid 

 plus oxalacetic acid. The rapid rates at which oxalacetic, alpha- 

 ketoglutaric, and pyruvic acids participate in non-transaminating 

 reactions make it highly doubtful whether reactions 3 and 6 ever 

 proceed fast enough to participate in the metabolism of these com- 

 pounds. This may not apply to liver and pigeon breast muscle. 



Among the possible metabolic reactions which transamination may 

 influence are those of protein and amino acid synthesis and degrada- 

 tion, glycolysis, and hydrogen transport. 



protein and amino ACm SYNTHESIS AND DEGRADATION 



Animal Tissues.— An attractive theory of amino acid synthesis and 

 degradation in plant and animal tissues has been proposed by 

 Braunstein (1). According to this theory amino acids are synthesized 

 or degraded by the transamination reaction in conjunction with the 

 glutamic dehydrogenase system of Euler et al. (27) and Dewan (50). 

 The latter system serves the two functions of synthesizing glutamic 

 acid for transamination with alpha-keto acids to yield new amino 

 acids, and of oxidizing the glutamic acid formed from alpha- 

 ketoglutaric acid and different amino acids. Both enzyme systems 

 are present in most tissues, although in varying amounts. Thus 

 transaminase is higher in muscle than in liver, whereas glutamic 

 dehydrogenase is higher in liver than in muscle. 



Braunstein and Bychkov (51) have reported production of am- 

 monia from Z( + ) -alanine when the latter is incubated with alpha- 

 ketoglutaric acid, glutamic aminopherase, glutamic dehydrogenase, 

 pyocyanine, and cozymase. About 12.5 per cent of the theoretical 

 yield was realized after three hours' incubation. These workers 

 pointed out that the above system is a cell-free model of Z-amino 

 acid dehydrogenase, which to date has not been demonstrated to 



