BIOSYNTHESIS 



251 



imidazole-glycerol, imidazole-hydroxy-acetone and their derivatives phos- 

 phorylated in the terminal position of the side chain. It is these phosphory- 

 lated derivatives and free histidinol that are intermediates in the synthesis 

 whose terminal operation, the conversion of histidinol to histidine, is 

 catalysed by a DPN-containing enzyme which has been isolated from 

 E. colt. When we come to the imidazole ring itself, experiments with 

 sotopes have shown that C-2 is derived from "formate". 



(s) Biosynthesis of Lysine 

 COOH 



COOH 



CH, 



CHXOOH 



Aspartic 

 acid 



+ 



a — ketoadipic 

 acid 



COOH 



I 

 CHNH, 



CH2 



CH2 



I 

 CH2 



*CHNH2 



*COOH 



a — aminoadipic 

 acid 



(moulds) 



CH2NH2 



CH, 



CHg (bacteria) 

 CH, 



CH, 



CH, 



CH, 



CHNH2 

 COOH 



lysine 



CHNH2 



COOH 



a,a'-diaminopimelic 

 acid 



Fig. 71 (Davis) — Biosynthesis of lysine. 



The biosynthesis of lysine forms an exception to the general run of 

 biosynthetic processes we have so far considered and which we have been 

 able to assume, at least in general outline, to be the same in all cells. Here 

 the comparative biochemist has found a field of study at the level of a 

 biosynthetic mechanism. The biosynthesis of lysine, in fact, differs in 

 moulds and in bacteria. In the former, the starting materials are acetate and 



