ANTIGENS AS BIOCATALYSTS 



1. The Chemical Nature of Antibodies 



Chemical tests have shown (Welsh and Chapman, 1908; Dean and 

 Webb, 1926) that the precipitates resulting from antigen-antibody 

 reactions contain considerably more protein than the antigen could 

 account for. A series of quantitative analytical studies (Hartley, 1926; 

 Felton and Bailey, 1926; Heidelberger and Kendall, 1929, 1933, 1935, 

 1936) have demonstrated that the precipitate obtained with protein- 

 free pneumococcal carbohydrates and immune sera consists largely of 

 serum globulin; 2.5 mg. of pneumococcal polysaccharide Type II 

 precipitated 37 mg. of protein. The serum proteins isolated from these 

 precipitates were found to be 98 per cent antibody. 



The properties of diphtheria toxin-antitoxin floccules and the pre- 

 cipitate in other types of antigen-antibody precipitation reactions 

 were similar to those of serum globulin (Marrack and Smith, 1930). 

 The particulate antigens, such as bacteria and red blood corpuscles, 

 when fully combined wdth antibody, moved in an electric field as 

 though they were pure globulin (Shibley, 1926; Eagle, 1930; Mc- 

 Cutcheon, Mudd, Strumia, and Lucke, 1930). 



The effect of proteolytic enzymes, such as pepsin, trypsin and 

 papain, on antibodies has constituted the subject of numerous in- 

 vestigations. These studies have shown that antibodies are destroyed 

 rapidly by pepsin, less rapidly by trypsin. Types I and II pneumo- 

 coccal antisera, and purified Types I, II, and III pneumococcal anti- 

 bodies were slowly destroyed by trypsin (Felton and Kauffmann, 

 1927). The precipitate formed by Type I pneumococcal polysaccharide 

 and antiserum was incubated with pepsin (pH 4.8). The destruction 

 of precipitin ran parallel to the increase of amino nitrogen (Chow, 

 Lee and Wu, 1937). Rosenheim (1935) found that the O-agglutinins 

 in all serum samples from three horses immunized with B. typhosus 

 were rapidly destroyed by pepsin (pH 4.6-4.8), trypsin (pH 8.6) and 

 activated papain. The H agglutinins in serum samples obtained from 

 each of three horses after the first immunizing course were rapidly de- 

 stroyed by proteolytic enzymes. Those in samples obtained after 

 several immunizing courses were not appreciably destroyed under 

 identical conditions. The H agglutinins which were apparently resist- 

 ant to pepsin and trypsin were not resistant to activated papain. The 



