1 20 IMMUNO-CATALYSIS 



quarters. The observed molecular weights of the quarters were 47,000, 

 though, on the basis of the molecular weight of 153,000 of the original 

 globulin particle, they should have been only 38,000. Although 90 

 per cent of the globulin was split into quarters, much antibody activity 

 was retained. The antitoxin activity of the whole digest was from 70 

 to 90 per cent of the undigested antitoxin when papain was used, and 

 100 per cent of the activity was retained when digestion was carried 

 out with bromelin. In another study, Peterman (1946) found that 

 human immune gamma globulin is split by pepsin into molecules of 

 half size. Further digestion yielded smaller particles and ultimately 

 dialyzable fragments. Immunological assays showed that in the digests 

 containing half size antibodies the typhoid "O" agglutinin was lost, 

 while the concentration of "H" agglutinin, of diphtheria and strepto- 

 coccus antitoxin and of anti-influenza A remained substantially un- 

 changed. 



In view of the above findings, one may expect that the specificity of 

 antibody molecules may reside in still smaller units derivable from the 

 quarter size digestion products. Dialyzable units of antibody may fail 

 to agglutinate bacteria, or precipitate antigens, but they may inhibit 

 the reactions between whole antigen and whole antibody. 



Our information concerning the structure of proteins may be ex- 

 panded if the smaller proteolytic or hydrolytic cleavage products are 

 isolated and characterized chemically and serologically. One may be 

 able profitably to employ the technique developed by Tiselius (1947) 

 and Martin and Synge (1945) for this purpose. The results of such 

 studies may have specific bearing on the debate on the valency of anti- 

 body molecules, and on the mechanism of antibody synthesis. 

 Conclusion. A consideration of the above experimental facts shows 

 clearly that biological specificities are inherent in the respective 

 chemical structures of proteins. The discussed material can be sum- 

 marized in the following manner: 



(a) The enzymes possessing minimum unit molecular weights of 

 about 15,000, that is the smallest molecular weight entities which 

 cannot reversibly be split or dissociated, are serologically and en- 

 zymatically distinct and different from the other proteins related to 

 them species specifically. 



(b) Polypeptides with molecular weights of about 6,000 show 



