62 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



In connection with histidine, the work of Windaus and Knoop on 

 the formation of methylimidazole from glucose must be mentioned on 

 account of the possible synthesis in the animal body of both histidine 

 and purine bases. 



It has long been known that glucose is converted by alkalies into 

 lactic acid and other oxy acids. Knoop and Windaus investigated this 

 reaction in the presence of ammonia in the form of the strongly dissoci- 

 ated zinc hydroxide ammonia. By exposing glucose and zinc hydrox- 

 ide ammonia to diffused daylight they obtained methylimidazole. 

 From the sugar glyceric aldehyde is probably first formed, and this is 

 converted into methyl glyoxal by loss of water, from which lactic acid 

 may arise by the subsequent addition of water. 



CH 2 OH . CHOH . CHO -> CH 3 .CO.CHO -> CH 3 . CHOH . COOH 



In the presence of ammonia and formaldehyde, also a product from 

 the sugar, methylimidazole is formed as follows : 



CH 3 . CO H 2 NH CH 3 C NH 



| CH 



CHO H 9 NH || \ 



>CH + 3 H 2 



O H CH-N 



This condensation with formaldehyde as well as with methyl glyoxal 

 is confirmed by the formation of dimethylimidazole when ammonia 

 acts upon glucose and acetaldehyde. 



CH 3 . CO H 2 NH CH 3 C NH 



CH II \ 



CHO H 2 NH || \ ^C . CH 3 + 3 H 2 O 



O CH 3 CH-N 



From imidazole by condensation with glycocoll and simultaneous oxida- 

 tion histidine may possibly be formed thus : 

 CH NH CH NH 



o_/ CH I/ 



CH 2 CH 2 



+ H 2 



+ 



H CH . NH 2 



CH . NH 2 COOH 

 COOH 



and by condensation with urea xanthine may arise : 



NH 2 3 O CH 3 NH CO 



CO + C NH CO C NH . + 3 HO 2 



\ 



CH 



\ 



CH 



NH 2 O CH N NH C N 



