THE PROTEINS 21 



Viewed from another standpoint the amino acids 

 may be divided into mono-amino acids, glycocoll, 

 alanine, valine, leucine, isoleucine, phenylalanine, tyro- 

 sine, serine, aspartic acid, and glutamic acid, each 

 containing, as the name implies a single amino (NH2) 

 group diamino acids, containing two amino groups, 

 as arginine, and lysine and finally the heterocyclic com- 

 pounds as histidine, proline, oxyproline, and trypto- 

 phane. 



THE QUANTITATIVE RELATIONSHIPS OF AMINO ACIDS 

 IN PROTEINS 



The most serious obstacle to the quantitative estima- 

 tion of amino acids in hydrolysis mixtures has been 

 that of inadequate methods of separation. By means 

 of the ester method of E. Fischer this difficulty has 

 been obviated in large measure. In Table I below are 

 presented figures showing the yield of individual amino 

 acids obtained by various investigators from repre- 

 sentative simple proteins. The figures have not all 

 been derived from use of the most exact methods of 

 isolation, hence it is probable that they may not repre- 

 sent maximal values or be strictly correct. Neverthe- 

 less, they are sufficiently suggestive to demonstrate the 

 distinct differences that exist between the simple 

 proteins. 



Table II undoubtedly gives the most accurate figures 

 obtainable at present for the quantitative yield of 



