130 PHYSIOLOGY 



The Pyrrol Ring which occurs in proline and in oxyproline 

 may possibly be derived from an open chain amino-acid, and it has, 

 in fact, been suggested that the proline found in the products of the acid 

 digestion of proteins is derived from or ni thine by a process of con- 

 densation with the loss of ammonia. Thus : 



CH 2 NH 2 . CH 2 . CH 2 . CH . NH 2 COOH becomes 

 OH 2 .CH 2 .CH 2 .CH.COOH 



NH 



or, as it is generally written : 



CH 2 CH.COOH 



\/ 

 NH 



Its pre-existence in the protein molecule is, however, practically 

 assured, and it plays an important part in the building up both of 

 chlorophyll and of hsematin, the prosthetic group of haemoglobin. 



CH NH, 



Iminazol || //^^- 



CH N 



occurs in histidine (which is iminazol alanine), and can be formed 

 fairly readily by the action of certain catalytic agents on a mixture of 

 glucose and ammonia. Thus, if a solution of glucose with ammonia 

 and zinc oxide be exposed to light, methyl iminazol is formed in 

 large quantities. Windaus and Knoop imagined that in this process 

 glyceric aldehyde and formaldehyde are first formed, and that these 

 then interact with ammonia to form methyl iminazol. 



CH 3 



C NH 



CH N 



It is interest ing to note that if we attach to this compound carbamide 

 or urea we obtain a body belonging to the class of purines. Xanthin, 

 for instance, would have a formula 



NH CO 



CO C NH X 



>CH 

 NH CH ] ' 



