PROTEINS. 77 



to 295 C., leucine decomposes with the formation of carbon 

 dioxide, ammonia and amylamine. Aqueous solutions of leucine 

 obtained from proteins are Isevo-rotatory, but its acid or alkaline 

 solutions are dextro-rotatory. So-called impure leucine 1 is a slightly 

 refractive substance, which generally crystallizes in balls having 

 a radial structure or in aggregations of spherical bodies, Fig. 104, 

 Chapter XX. 



Isoleucine, C 6 H 13 NO 2 . Isoleucine is a-amino-methyl-ethyl-pro- 

 pionic acid, and possesses the following structural formula: 



CH a NH 2 



COOH. 

 H 



v-/-*-j-2 2 



CH C-i 



A, 



This amino acid was recently discovered by Ehrlich. Its presence 

 has been established among the decomposition products of only a 

 few proteins although it probably occurs among those of many or 

 most of them. Ehrlich has shown that the d-amyl alcohol which 

 is produced by yeast fermentation originates from isoleucine and 

 the isoamylalcohol originates from leucine. Isoleucine is dextro- 

 rotatory. 



Lysine, C 6 H 14 N 2 O 2 . The three bodies, lysine, arginine and his- 

 tidine, are frequently classed together as the hexone bases. Lysine 

 was the first of the bases discovered. It is a-e-diamino-caproic acid 

 and hence possesses the following structure : 



NH 2 H H H NH 2 

 H-C - 0-C-C-C-COOH. 



i 4m 



It is dextro-rotatory and is found in relatively large amount in 

 casein and gelatin. Lysine is obtained from nearly all proteins but 

 is absent from the vegetable proteins which are soluble in strong 

 alcohol. It is the mother-substance of cadaverin and has never 

 been obtained in crystalline form. Lysine is usually obtained as 



1 These balls of so-called impure leucine do contain considerable leucine, but 

 inasmuch as they may contain many other things it is a bad practice to allude 

 to them as leucine. 



