THE PRECURSORS OF UREA 665 



urea. There is nothing inherently improbable in such a synthesis 

 taking place as a final step in proteid katabolism. Similar final 

 syntheses are well known in the production of hippuric acid, the 

 ethereal sulphates, and the conjugated compounds of glycuronic 

 acid. 



(2) DrechseVs view; the origin of urea from arginin. He 

 showed that urea could be directly produced from proteids by 

 heating them for a long time with baryta. He found that the 

 intermediate step in this direct conversion was formed by a basic 

 body, lysatin, which he produced by hydrolysing proteid with an 

 acid, and which yielded urea when heated for half-an-hour with 

 baryta. Hedin showed that lysatin was a mixture of the two 

 hexone bases, lysin and arginin, and that the urea was derived 

 only from the arginin, which splits on hydrolysis into urea and 

 ornithin. 



NH 2 



NH:C 



NH - C 3 H 6 . CH . NH 2 . COOH + H 2 O 



(Arginin} 



= CO(NH 2 ) 2 + NH 2 . C 3 H 6 . CH . NH 2 . COOH. 

 (Urea) (Ornithin) 



This reaction is of considerable theoretical importance. 



It has been shown that the combinations of C within the 

 proteid molecule occurs probably in two types. The first is seen 

 in hippuric acid and the synthetic polypeptides of Fischer. In 

 this type a single NH group unites two C chains together and 

 has a CO group next to it (1). The second type consists of a 

 guanidin group NH . C . NH which either joins as before two 



NH 



C chains together (2), or is at one end of a carbon chain (2 X ). 



(1) -CO.NH.C- 



(2) -CO.NH.C.NH.C- 



NH 



(2') NH 2 . C . NH . C - 

 NH 



Hydrolysis of (1) or (2) by acids splits off only the CO group, 



