MOLECULAR COMPLEMENTARINESS IN ANTIGEN-ANTIBODY SYSTEMS 



Fig. 2. \'an dcr Waals outline of ort/io, vuia and /^ara-azobenzenearsonates 



antibodies directed against both groups. Thus, even though both determinants 

 are present in the antigen in close juxtaposition and in ecjual quantities, indi- 

 vidual antibodies are formed against individual parts. 



For an example of an antibody formed against a simple substance, let us 

 look first at antibodies formed against the azobenzenearsonate ion (Pressman 

 and Siegel, 1953). Fig. 2 shows the para, meta and ortho azobenzenearsonates. 

 The outer line is the van der Waals outline of the molecule. 



When antibodies are formed against any one of these, they act as though 

 they were formed against the van der Waals outline of the hapten as a tem- 

 plate. They can also combine with an unsubstituted benzenearsonate ion. 

 Substituents on the benzenearsonate decrease the extent of combination when 

 they interfere sterically. 



Thus, for antibodies to the /^-azobenzenearsonate group, substituents in the 

 ortho or meta positions decrease combining power generally. If we place a sub- 

 stituent in the para position, we might expect an increased combination of the 

 hapten with the antibody, because the antibody would have a region which 

 has been formed against the azo group and this region can also accommodate 

 some other substituent. 



In the case of antibody to the we/u-azobenzenearsonate, there would be 

 steric effects observed for substituents in all positions except the meta position. 

 In the case of antibody to the or///o-azobenzenearsonate, there would be ob- 

 served steric effects of substituents which are in the jneta or para position. 

 Substituents in the ortho position, however, would fit in the region of the anti- 

 body which was formed to accommodate the azo group. 



The results of studies obtained from these three systems are shown in Fig. 3. 

 Values are listed for the relative combining constant, Ko, which is the com- 

 bining constant of the substituted benzenearsonate relative to the combining 

 constant of the unsubstituted benzenearsonate in these various systems (Paul- 

 ing, Pressman and Grossberg, 1944). The various substituents used are listed, 

 and it can be seen that with the antibody against the r>r///()-azobenzenearsonate 

 we get the best combination with the ortho substituted compounds, interme- 



