SYNTHESIS OF AMINO-ACIDS 63 



Synthetic pyridoxamine phosphate activated some prepara- 

 tions of partially resolved bacterial transaminases [48], and 

 though first reported not to restore activity to a resolved 

 preparation of the pig heart glutamic-aspartic transaminase, 

 later workers showed that it was as active as pyridoxal phos- 

 phate provided it was incubated with the apoenzyme for 

 30-60 minutes before adding the substrates [366]. Gunsalus 

 and Tonzetich have recently demonstrated that prepara- 

 tions oiEsch. coli catalysed transamination reactions between 

 pyridoxal and glutamic acid and between pyridoxamine and 

 a-ketoglutarate. Hence, while there is some reason to believe 

 that the prosthetic group of the transaminases can function 

 a£ a carrier of amino groups, direct proof that it does so has 

 still to be obtained. 



Owing to the lack of essential data, it is not yet possible 

 to assess whether transamination is of key importance in 

 amino-acid synthesis. The available information, admittedly 

 extremely incomplete, indicates that the transaminases are 

 widely distributed in micro-organisms, at least in those non- 

 exacting to amino-acids. Whether or not there is a complete 

 series of enzymes capable of reacting with the keto acids 

 corresponding to all the natural amino-acids is still not 

 known. If transamination is involved in the synthesis of an 

 amino-acid, then it follows that the organism must be able 

 to synthesize the appropriate keto acid. Except for pyruvate, 

 oxaloacetate and a-ketoglutarate, virtually nothing is known 

 about the synthesis of these compounds, and although the 

 two former acids are known to be produced in the inter- 

 mediary metabolism of many organisms, conclusive evidence 

 of the ability to synthesize a-ketoglutarate is only available 

 for Ps. fluorescens, Az. agilis and Sac. cerevisiae. Although in 

 recent years it has been thought that glutamic acid was the 

 only amino-acid able to transfer an amino group to a wide 

 variety of keto acids, there is now some evidence that 

 aspartic acid can transaminate with acids other than a-keto- 

 glutarate, e.g. there is an aromatic amino-acid — aspartic 

 acid transaminase in Esch. coli [39^]. Furthermore, trans- 

 amination reactions are now known in which dicarboxylic 

 acids do not participate, e.g. Brucella abortus appears to 



