MECHANISM OF ANTIBODY FORMATION 83 



antibody. The specific combining capacities of antigens reside, there- 

 fore, in the whole as well as in its component small molecular weight 

 non-antigenic units. These units carry specific configuration and 

 chemically reactive groups. On the basis of these established facts one 

 may conclude that while the specific combining capacities of antigens, 

 or their component units, are dependent on the amino acid composition 

 and order of their linkage yielding specific configuration to each protein 

 molecule, the antibody producing catalytic activity depends on the 

 integrity of the whole molecule. 



The interdependence between catalytic activity of antigen and its 

 minimum irreducible molecular unit size is a common and basic 

 property of enzymes, hormones and viruses also. No doubt, the speci- 

 ficities of the latter three are similarly dependent on the amino acid 

 composition and order of their linkage yielding specific configuration 

 to each species of protein molecule. 



These facts may perhaps more fully be appreciated if we consider the 

 fact that the specific activities of the same heme group in various 

 closely related enzymes, cytochromes, cytochrome oxidase, cytochrome 

 peroxidase and catalase, are directed by specific protein carriers. 

 Similarly, there exist distinct differences in antigenic specificity of 

 closely related classes of proteins. One can cite as an example dif- 

 ferences in this respect of a class of a-, (3- and y-globulins from the same 

 species of animal. Kendall (1937, 1938) showed that these globulins 

 of human serum are antigenically specific. The antibodies against these 

 globulins were found to be specific for each of these globulins; that is, 

 the a-globulin antiserum reacted with the a-globulin to give a precipi- 

 tate, but did not react with fS- or y-globulin, with albumin, or with any 

 other component of human serum. Thus, this highly refined im- 

 munological differentiation of the closely related globulins of human 

 serum, which differ from each other in amino acid composition 

 (Table II), electrical mobility, molecular weight, viscosity and iso- 

 electric point, makes the correlation between the structural pattern 

 and the biological specificity of the proteins reasonably plausible. 



