ANTIGENS 41 



When Landsteiner tested antibodies to larger peptides, he stiil 

 found that cross-reactions occurred with peptides having the same 

 terminal amino acids, but such cross-reactions did not always occur, 

 and some cross-reactions were found to be due to common amino 

 acids in other positions. The cross-reactions were definitely related 

 to similarities of constitution (Table 3-1). For instance, an antibody 

 for the pentapeptide GGGGG, where G stands for glycine, precipitated 

 — GG but not — LG antigen, where L stands for leucine, and pre- 

 cipitated much less — LGG than — GGG. The amount of precipitate 

 produced by an anti-GGGGL antiserum with various peptide-con- 

 taining antigens increased in the order — L, — GL, — GGL, — GGGL, 

 -GGGGL (Table 3-2). 



TABLE 3-2 

 Increase in Strength of Cross-Reactions with Increase in Length of Hapten" 



" Landsteiner, 1945. 



'' G = glycine, L = leucine. 



The strongest reactions were not always obtained with haptens 

 having the terminal portions identical with those of the immunizing 

 hapten. For instance, when Landsteiner prepared antisera against 

 polypeptides in which the terminal carboxyl group had been con- 

 verted to the amide (Fig. 3-4) he found than an antiserum for 



HjX^^ ^CONHCH2CONHCH,CONH,. 



Fig. 3-4. Amide of /'-aminobenzoylglycylglycine. 



GGLGGAm reacted with — GGLAm and — GGGGLAm but not 

 with — LGGAm (Table 3-3), in spite of the fact that the terminal 

 three units of this last hapten are identical with the terminal three 

 units of the immunizing hapten. Landsteiner attributed this to a 



