172 PHYSIOLOGY 



Recent work by Neubauer tends to show that deamination is 

 accompanied in the first place by oxidation, so that the first inter- 

 mediate product formed is not an a oxy-acid, but an a ketonic acid. A 

 second atom of oxygen is then taken up, and carbon dioxide is split 

 off, with the production of the next lower acid of the series. 



We might represent these changes as follows : 



(1) CH 3 CH 3 



CH 3 



CHNH 2 + = CO + NH 

 COOH COOH 



(2) CH 3 



CO + = + C0 2 



COOH 

 COOH 



Is the reverse change ever effected in the animal body ? If it 

 were possible to replace the OH group in an oxy-fatty acid by NH 2 or 

 the in an a ketonic acid by HNH 2 , it ought also to be possible to 

 nourish an animal from a mixture of carbohydrates and ammonia, 

 or at any rate by supplying him with a mixture of the appropriate 

 oxy-acids or ketonic acids and ammonia. Until recently there was 

 no evidence that the animal body is able to utilise nitrogen, except 

 in organic combination as amino-acids or the complex aggregate of 

 amino-acids known as proteins. In the plant the process of synthesis 

 of protein from ammonia and a carbohydrate such as hexose is con- 

 tinuously going on, and it is probable that the formation of amino- 

 acid occurs by a process the reverse of that which we have just been 

 studying. Knoop has shown that the same reversed change may occur 

 even in a mammal, and that here again the intermediate substance is an 

 a ketonic acid. On administering benzylpyrotartaric acid (C 6 H 5 . 

 CH 2 .CH 2 .CO.COOH) to a dog, a certain amount of benzylalanine 

 (C 6 H 5 .CH 2 .CH 2 .CHNH 2 .COOH) appeared in the urine. The first 

 phase of the oxidative deamination of amino-acids is thus a reversible 

 one and may be represented : 



R R R 



I I /OH ! 



CHNH 2 + C< CO -f Mi 3 



| | NH 2 



COOH COOH COOH 



(3) DECARBOXYLATION. Many amino-acids when subjected to 



