228 BACTERIOLOGICAL CHEMISTRY 



cultures on pure amino -acids was investigated, but still 

 it was impossible to connect the action of any one organ- 

 ism, for instance, with the formation of any particular 

 type of product. Finally, Harden and Ehrlich instituted 

 the present stage by studying the effect of pure cultures 

 of a single organism on single pure amino -acids. 



If we take R.CH2.CH.NH2.COOH as representing the 

 structure of an amino -acid, the various types of break- 

 down which it may undergo can be summarised as 

 follows : — 



A. Decarboxylation to give the Amine. 



R.CH2.CH.NH2.COOH > R.CH2.CH2.NH2 + C()2. 



This type of breakdown is apparently only accomplished 

 by bacteria, and is favoured by anaerobic conditions. As 

 an example, Ps. fluorescens breaks down glycine to give 

 methylamine . 



B. Deamination. 



{a) Reductive to give Saturated Acids, 



H2 

 R.CH2.CH.NH2.COOH — > R.CH2.CH2.COOH + NH3. 



The products will be seen to be substituted propionic 

 acids ; tryptophane gives indole -propionic acid : — 



^\ CH2.CH.COOH ^\ CH2.CH2.COOH 



I !l II I I II II 



[ !l II NH2 > \ II II + NH3 



NH NH 



The hydrogen accepting amino -acid in the " Stickland 

 reaction " (see p. 218) undergoes reductive deamination, 

 at the expense of the second amino -acid which undergoes 

 oxidative deamination (B.(d), p. 230). Thus glycine gives 

 acetic acid and ammonia,, ornithine gives a» -amino - 

 valeric acid and ammonia whilst Z-proline also gives 

 CO -amino -valeric acid but no free ammonia. Here the 

 opening of the ring is equivalent to deamination, the 

 difference being that the freed amino group is held by 

 the other end of the chain : — 



