THi: MIT\l:n|.l-M OF PROT] IN 603 



by the Van Slyke method; hut in other cases, as in arginine, it fails to 

 give this and the other characteristic reactions of the amino group. That 

 the extra amino group in lysine reacts directly with nitrons acid explains 

 why various proteins when examined for amino nitrogen yield an amounl 

 that is equal to half of the lysine nitrogen. 



It will further be observed thai the amino acids are arranged in thi 

 main groups: one basic, another neutral, and the third acid. TJu adds 

 of Hi< basic group are three in number and have an alkalinity similar to 

 thai of ammonia. Thej have been called the hexom bases, because e 

 contains six carbon atoms. They are alone presenl in certain forms of | 

 triii called protamines. The neutral amino acids contain one amino group 

 and one carboxyl group, which exactly neutralize each other. This is 

 thf largest 'jroiip of amino acids, and is further subdivided into thi 

 one containing aromatic or benzene rings and including the very im- 

 portant amino acids, tyrosine and tryptophane; another containing 

 so-called pyrrolidine ring; ami the third, the largest of all, containing 

 the so-called aliphatic chains; that is. the chains characteristic of the 



fatty acids and which may he cither straighl Or branched. When the chains 



are branched, the substance is called an isosubstance, as in isoleucine. 

 The acid amino acids, including glutamic acid and aspartic acid, are 

 characterized by containing two carboxyl groups and only one amino 

 group. They therefore resemble acetic acid in acidity. 



Tt may be of assistance to some if Ave restate those chemical facts 

 from a Blightly different standpoint as follows: 



Glycine, or glycocoll, is amine:, 1. I Ml Nil <'< K)H. 



Ml 



/ 

 Alanine is glycine plus a methyl group, i'll«'ll : it u therefore amino- 



\ 



N 'II 



/ 



propionic acid run! ia closely relate. l to lactic acid, which ia f'lH'H . Mem 



\ 



booH 



the Other amino acid* may f alanin 



1. s, rinr is alanine with an "OH" (hydros tup in | the ••II*' 



Nil 



/ 



alums of the moth} 1 gi oup, < !H ( " ' CH 



\ 

 OOOB 



_ ' <■ ia alanine with an "8H" tliio) group in thii 



Nil 



/ 



CH 8H <'ll 



\ 



COoii 



