58 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



The identity of the arginine obtained from animal proteins with that 

 from vegetable proteins was at first denied by Gulewitsch, but a little 

 later he showed that they were identical, as also did Schulze. 



The arginine, as it occurs in the proteins, is the dextro-rotatory 

 modification except in fibrin, from which both Kutscher and Cathcart 

 have isolated the inactive form. 



Schulze and Likiernik, in 1891, found that urea was formed when 

 arginine was heated with baryta ; they therefore supposed that arginine 

 was a derivative of guanidine. In 1897 Schulze and Winterstein found 

 that ornithine was also formed ; they isolated it as its dibenzoyl deriva- 

 tive, which was found to be identical with Jaffe's ornithuric acid. 

 Ornithine was regarded as a diaminovalerianic acid ; Schulze and 

 Winterstein showed that it contained two NH 2 groups not attached to 

 neighbouring carbon atoms, and suggested that arginine, as it was a 

 derivative of guanidine and ornithine, might have the following constitu- 

 tion : 



NH 2 NH 2 



NH = C NH CH 2 CH 2 CH 2 CH COOH 



and that the formation of urea and ornithine might be explained accord- 

 ing to the equation : 



NH 2 NH 2 



NH = C NH CH 2 CH 2 CH 2 ~CH COOH + H 2 O = 



NH 2 NH 2 



NH 2 C = O+ NH 2 CH 2 CH 2 CH 2 CH COOH 



Schulze and Winterstein, in 1899, proved that arginine was S-guani- 

 dine-a-aminovalerianic acid by synthesis from cyanamide and orni- 

 thine : 



NH 2 

 H 2 N CH 2 CH 2 CH 2 CH COOH + CN NH 2 = 



NH.J NH 2 



NH = C NH CH 2 CH 2 CH 2 CH COOH 



The presence of a guanidine group in arginine is also proved by the 

 formation of guanidinebutyric acid and of guanidine and succinic acid 

 by oxidation with permanganate, which probably takes place according 

 to the following equations (Kutscher) : 



