THE PROTEINS 83 



Aspartic acid was first found in the shoots of asparagus in the form of the amide 

 asparagine : 



COOH 



I 

 CHNH 2 



CH 2 



CONH 2 



This substance is very widely distributed throughout the vegetable kingdom and 

 is present in seedlings in very large quantities, as much as 25 per cent, of the di i. d 

 weight. In plants it apparently serves either as a reserve material or as the form 

 in which the greater part of the nitrogen is conveyed from the reserve organs to be 

 built up into the protoplasm of the growing parts of the plant. 



(3) Diamino-acids 



Of these two are known, namely, lysine and ornithine. Owing to the 

 presence of two NH 2 groups in their molecule, they possess marked basic 

 characters, and are precipitated from the acid solution obtained by the 

 hydrolysis of proteins on adding phosphotungstic acid. Since lysine, argi- 

 nine, and histidine (another amino-acid which will be described later) all 

 contain six carbon atoms in their molecule, these three bodies were classed 

 together by Kossel as the ' hexone ' bases. Apart, however, from their high 

 content in nitrogen, the chemical resemblance between these bodies is no 

 closer than between them and the other members of the amino-acid series. 



Another body isolated by Fischer in small quantities is supposed to 

 belong to this class and to have the composition diamino-trioxydodecoic acid. 



LYSINE C 6 H 14 N 2 2 is a-e-diamino-caproic acid having the formula 



CH 2 NH 2 



(CH 2 ) 3 

 CH.NH 2 



COOH 



ARGININE, which was first discovered in plants (the cotyledons 

 lupins), is not a simple amino-acid, but a compound of an amino-acid wit] 

 guanidin. If boiled with baryta water it splits up into urea and a subs 

 reacting as a base which was called ornithine.* 



ORNITHINE, diamino-valerianic acid, has the formula 



CH 2 NH 2 



(CH 2 ) 2 

 CH.NH 2 

 COOH 



* Ornithine had b3en previously discovered in the urine of fowls after I 

 stration of benzoic acid, in the form of an acid known as ormthunc a 



