SYNTHESIS OF AMINO-ACIDS 6l 



RiCH(NH,)COOH+R2COCOOH ^ 



RiCOCOOH+R2CH(NH2)COOH (i) 



Reactions of this type were first discovered in animal tissues 

 by Braunstein and Kritzmann, who concluded that the 

 amino groups of several amino-acids could be transferred 

 in such a manner provided one of the participants in the 

 system was a dicarboxylic acid, i.e. aspartic, glutamic, 

 oxaloacetic, or a-ketoglutaric acid [4]. Cell-free preparations 

 of what were believed to be two distinct transaminases were 

 obtained, one catalysed reactions ii and iii, and the other 

 reaction iv: 



glutamate+ pyruvate ?^ a-ketoglutarate+ alanine (ii) 



glutamate+oxaloacetate ^^ a-ketogIutarate+ aspartate (iii) 



aspartate + pyruvate ?=i oxaloacetate+ alanine (iv) 



Later workers isolated two enzyme systems, specific for re- 

 actions ii and iii respectively, and Kritzmann 's second trans- 

 aminase was shown to be an artifact and due to a mixture 

 of these two enzymes with catalytic amounts of glutamate 

 functioning as a carrier between the two systems [23]. 



Similar transaminase systems were later found in bacteria, 

 yeasts [39^] and Neurospora [17^, Z>]. Washed cell suspensions 

 of various bacteria (staphylococci, streptococci, pneumo- 

 cocci, enterobacteria, Az. agilis, and Ps. pyocyanea) cata- 

 lysed the transfer of the amino group of glutamic acid to 

 oxaloacetic acid (reaction iii), and cell-free preparations of 

 Strep, faecalis accomplished both reactions ii and iii, the 

 equilibrium being in favour of the synthesis of alanine and 

 aspartic acid respectively [34, 35]. Like the animal trans- 

 aminases, the bacterial enzymes possess a prosthetic group 

 of pyridoxal phosphate. The glutamic-aspartic trans- 

 aminase of Strep, faecalis had been partially resolved and 

 activity was restored by the addition of synthetic pyridoxal 

 phosphate or natural codecarboxylase. The advent of paper 

 chromatography has facilitated the detection and identifica- 

 tion of small quantities of amino-acids and has been used 

 to demonstrate that several amino-acids can transfer their 

 amino groups to a-ketoglutarate. These experiments have 

 been performed with Esch. coli, Ps.fluorescens, B. suhtilis [14] 



