16 DAVID PRESSMAN 



of a benzene ring, acts as though it were a CBr or some other large grouping. 

 This apparent steric effect of the nitrogen atom in the ring fits in with the con- 

 cept that the nitrogen is hydrated in aqueous solution in these compounds and 

 the hydration is strong enough to affect the interaction of these molecules in 

 biological systems. 



Since in nearly all biological systems the reactions take place in aqueous 

 solution, the hydrated configuration of various ions is of extreme importance 

 and may be the determining factor in molecular specificity in these systems. 



In conclusion, I want to point out that antigen-antibody systems resemble 

 enzyme-substrate systems and other systems of biological interaction in which 

 there are rigorous requirements of configuration and charge for specificity, and 

 that they are being used to yield information about the configuration of sub- 

 stances of biological interest in aqueous solution. 



References 



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Landsteiner, K. 1945. The Specificity of Serological Reactions. Rev. Ed. Cambridge, 

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Landsteiner, K. and J. Van der Scheer. 1938. Cross reactions of immune serums to 

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Marrack, J. R. and F. C. Smith. 1932. Quantitative aspects of immunity reactions: 

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Pauling, L., D. H. Campbell and D. Pressman. 1943. The nature of the forces be- 

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Pauling, L., D. Pressman and A. L. Grossberg. 1944. The serological properties of 

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Pressman, D. 1953. Antibodies as specific chemical reagents. .Adv. in Biol, and Med. 

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Pressman, D., J. H. Bryden and L. Pauling. 1948. Reactions of antiserum homologous 

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Pressman, D., J. T. Maynard, A. L. Grossberg and L. Pauling. 1943. Serological 

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