THE PRECURSORS OF UREA 667 



guanidin radicle and produce urea. Such a ferment has been 

 described by Kossel and Dakin and called arginase. 



Arginase in a few hours splits arginin, a compound of a 

 guanidin radicle with a. amino-valerianic acid, into urea and 

 orinthin (diamino-valerianic acid). This ferment has been found 

 in greatest quantity in the liver, in less quantity in the kidneys, 

 thymus, lymphatic gland, and mucous membrane of the ali- 

 mentary canal, and possibly in the blood and muscles. It 

 appears to be absent from the spleen, suprarenals and pancreatic 

 juice. Arginase is not capable of attacking such simple proteids 

 as the protamins, and is presumably therefore incapable of 

 splitting urea from the more complex proteids. This ferment 

 can explain only the second step in Drechsel's view, the pro- 

 duction in the tissues of urea from arginin. But the proteolytic 

 tissue ferments have been found to produce arginin during the 

 autolytic decomposition of tissue proteids. It is possible, there- 

 fore, to imagine the production of urea from proteid taking 

 place in the tissues in two stages as the result of the action of 

 two tissue ferments. 



The possibility exists, however, that the tissues may contain 

 a ferment capable of splitting off urea or some such body direct 

 from proteid. For Kossel and Dakin have described a ferment 

 in the wall of the small intestine which can attack the arginin 

 groups contained in a protamin in such a way that the ornithin 

 portion of the arginin remains attached to the rest of the proteid 

 molecule. It is not yet known in what form the guanidin radicle 

 of the arginin is split off, whether as urea, guanidin, or some 

 similar body, nor have they yet shown whether this ferment can 

 attack in the same way proteids more complex than protamins. 

 Kutscher and Otori have shown that guanidin is produced 

 during the autolysis of the pancreas, presumably by the action 

 of a ferment. They have found that it is also produced when 

 gelatine, arginin, or guanin, derived from nucleo-proteid, are 

 oxidised with a permanganate. They suggest that it is a product 

 in normal tissue metabolism and might have three possible fates 

 in the body. It may pass out unchanged in the urine and up 

 to now have escaped detection ; it may be converted into urea, 

 possibly by arginase ; or in the muscles it may be synthesised 

 into kreatin, for in them arginase is either not present at all, or 

 only in very "small quantity. 



