92 PHYSIOLOGY 



(3) Diamino-acids 



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

 the presence of two NH 2 groups in their molecule, they all possess 

 marked basic characters, and are precipitated from the acid solution 

 obtained by the hydrolysis of proteins on adding phosphotungstic 

 acid. Since lysine, arginine, and histidine (another aniino-aeid 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-triozy- 

 dodecoic acid. 



LYSINE 6 H 14 N 2 2 is -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 of 

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

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

 substance reacting as a base which was called ornithine.* 



ORNITHINE, diamino-valerianic acid, has the formula 



OH 2 NH 2 



(CH 2 ) 2 



CH.NH 2 



COOH 



The constitution of arginine is analogous to that of creatine, one ol 

 the most abundant nitrogenous extractives of muscle. 

 CREATINE has the formula 



HN = C ; N(CH 3 )CH 2 COOH 



H 2 N! 



* Ornithine had been previously discovered in the urine ol' fouls, after the 

 administration of benzoic acid, in the form of an acid known as ornithuric acid. 



