MODIFUCD AND CONJUGATED ANTIGENS 335 



Conjugated Antigens of Landsteiner. — Divzo Compounds. — By 

 diazotization is meant the treatment of an aromatic amino com- 

 pound -witli nitrous acid and hydrocliloric acid in the cold. As a 

 rule Landsteiner diazotized com})ounds that he wished to add to liis 

 proteins. It is very difficult to determine just where the diazonium 

 chloride would couple to the protein molecule. From the stand- 

 point of pure oi'^anic chemistry, however, the coupling of the 

 diazonium chloride with the tyrosine w^ould be most logical, since 

 this is in direct accord with the common procedure for making 

 azo dyes. Students of organic chemistry will recall that plienols 

 couple with phenyl diazonium chloride with the greatest of ease. 

 For example, Landsteiner diazotized p-aminobenzenesulphonic acid 

 by adding nitrous acid (NHOJ and hydrochloric acid (HCl) in 

 the cold; water split off and the diazonium chloride resulted: 



O 



HO— S— Z' ^— N i"H;T0T=N— ! OH ■+ H' i CI 



I! ^ ^ -'- ' '■ ' 



o 



o 



HO— S— (f ^— N=X— CI + 2H,0 



II ^ ^ 



O 



Coupling With a Protein. — This diazonium cldoride could be 

 coupled to a i)rotein since it wnll unite Avith tyrosine and perhaps 

 also other parts of the protein bj' replacing tlie hydrogen next to 

 the hydroxyl (-0H) group on the benzene ring, as is illustrated 

 below with tvrosine: 



O 



HO-^ H H O 



HO— s— / \— N=N— r'cr+ HH— . . 



II \ / '■ \/ 



-C— C— C— OH 



O H NH, 



The chloride of diazotized Tyrosine 



p-aminobenzenesulphonic acid. 



Arsonic Haptens. — In the same w^ay he diazotized p-aminoben- 

 zenearsonic acid and coupled it with proteins forming a new anti- 

 genic compound : 



