342 IMMUNOLOGY 



it will be observed to have both a basic (-NH^) and an acidic 

 (-COOH) group. Thus, reacting as an alkyl amine it yields 

 salts with acids and as an acid forms salts with bases. If the 

 ionizable hydrogen is replaced by an ethyl group to form the 

 ethyl ester, then the acid properties are destroyed and the basic 

 properties are dominant, so that it might unite through the 

 basic (-NHo) group with the acid (-COOH) groups of proteins. 

 The formula for the ethyl ester of amino acetic acid is 



H O 



H— C— C— OCH^ 



I 

 N— H 



I 

 H 



l\EMo\"AL OF Basic I'roperties of ax Amino Acid. — On the other 

 hand, if the same amino acid (amino acetic acid) is acetylated, a 

 compound is formed in which one of the hydrogens of the basic 

 (-NHo) group is replaced by the acetyl group, the formula for 

 the resulting compound being 



H o 



H— C— C— OH 



I 

 N— C— CH., 



H O 



In this ease the basic property is lost witli a simultaneous in- 

 crease in acid property- so that the latter Ixx'omes dominant and 

 union through replacement of the ionizable hydrogen to basic 

 groups of other amino acids may occur and thus a new compound 

 be formed through union with the salt-forming groups. 



Other Ways of Salt Formation. — Another way in which salts 

 may be formed may be illustrated as follows : 



If one diazotizes p-aminocinnamic acid by means of nitrous 

 and hydrochloric acids, there is obtained diazotized p-aminocin- 

 namic acid which will couple Avith the nucleus of tyrosine as 

 follows : 



