ALBUMINS OR PROTEINS. 



227 



its components. These investigators also succeeded in showing that the 

 splitting off of urea was due to the action of a specific ferment which they 

 called arginase. This ferment has been isolated from the liver, kidneys, 

 thymus and lymphatic glands, and the chopped-up intestine of the dog. 

 Small amounts are also present in the blood and muscles, but it is absent 

 in the suprarenal glands, in the spleen, and in the pancreatic juice. The 

 formation of urea from arginine proceeds according to the following scheme : 



/NH 2 

 C = NH NH 2 



V NH . CH 2 . CH 2 . CH 2 . CH . COOH + H 2 O 



Arginine 

 / NH 2 NH 2 NH 2 



= C = O + CH 2 . CH 2 . CH 2 . CH . COOH 



Urea Ornithine (Diaminovaleric acid) 



Now arginine is formed in the alimentary tract by the action of trypsin, 

 and we can easily imagine that this diamino acid is also formed in the 

 tissues by the breaking up of the proteins. One of the sources of urea is, 

 therefore, explained by this discovery. But the proteins used as food- 

 material contain far less arginine than they do of protamines. Only the 

 smallest part of urea present in the urine can originate from this source, 

 as the following table shows: 



Another interesting discovery accompanied the conclusion that urea 

 was split off from arginine in the tissues ; namely, the formation of ornithine. 

 Jaffe had already proved that as a matter of fact this diamino valeric acid 

 is formed in the organism, by showing that ornithuric acid was excreted 

 when benzoic acid was fed to birds. Ornithuric acid is the dibenzoyl 

 derivative of ornithine, and has the formula C5Hi (C 6 H 5 CO) 2 . N 2 O 2 . 

 The intermediate product of metabolism, ornithine, is undoubtedly 



