MODIFIED AND CONJUGATED ANTIGENS 343 



O H H ^^-| I H H O 



HO— C— C=C— / \— N=N— rcYTH'"!— I I— C— C— C— OH 



H NH, 



Now this prodiK't may uiiilo with the -NIL fjroiip of anotlier 

 amino aeid either by replacement of a hydrogen throupjli loss of 

 water to form an acid amide mroupins' as shown, 



H0-/\ 

 H O H H 



R— N— r hT" HO "i— C— C=C— / \— N=N- 



H H O 



I I !! 



C— C— C— OH 



H NH, 



or by simple addition to form a substituted ammonium salt as 

 shown by the fomiula 



H0-/\ 

 H H O H H 



\y il I I / — \ 



R— N— O— C— C=C— <^ ^— N=N— 



H H O 



I I II 

 — C— C— C— OH 



H H NH, 



Effect of Esterification and Methylation of Protein. — ^Land- 

 steiner (1917, 1918) brought about esterification of protein by 

 use of alcoholic acid solution, methylation by use of diazomethane 

 and acetylation by means of acid anhydrides or acid chlorides. 



Cross Reactions. — Proteins thus altered showed marked anti- 

 genic specificity depending upon the hapten introduced. Thus 

 methylated horse protein reacted with immune sera for methyl- 

 ated i")roteins from other species of animals as well as with meth- 

 ylated plant proteins. This indicated that the hapten influenced 

 the specificity of the protein-hapten complex. In the course of 

 his studies he found that among the proteins coupled with di- 

 azonium derivatives different phenomena Mere noted. 



Specific Reactions. — When he used them as antigens, those con- 

 taining aniline, p-amino-azobenzenesulphonic acid, ortho-, meta-, 

 and para-aminocinnamic acid and aminoazobenzenedisulphonic 

 acid stinuilated the production of specific antibodies reacting only 

 with the homologous antigens, while others showed a broader 

 sphere of activity. 



