MECHANISM OF ANTIBODY FORMATION 115 



two inhibitors can be subjected to hydrolytic cleavage to yield poly- 

 peptides comparable with those isolated from pancreas and serum 

 (Schmitz, 1938). 



Landsteiner and Chase (1933) showed that the reaction between 

 the antigen, sheep serum, and its homologous antibody could be in- 

 hibited by a readily dialyzable albumose obtained from the products of 

 peptic digestion of the coagulated sheep serum antigen. Landsteiner 

 (1942) reported also that the products of silk hydrolysis consisting of 

 peptides having molecular weights from 600 to 1,000 were capable 

 of inhibiting the reactions of precipitin sera for silk. From these results 

 Landsteiner inferred that silk fibroin contains determinant structures 

 of not more than eight to 12 amino acids. Holiday (1939) immunized 

 rabbits with horse serum albumin which was purified by electrophoresis 

 and shown to be homogeneous in the ultracentrifuge. The purified 

 antigen was digested with 1/4000 parts by weight of pepsin at pH 2.0 

 for periods of five and 30 minutes. 



In electrophoretic analysis the five minute digest, showed two com- 

 ponents with mobilities different from that of the intact antigen, and 

 by ultracentrifugation these components were inferred to have a size 

 14 that of the original molecule. The 30 minute digest showed the 

 components to be of Vs the size of the intact antigen. The V4 size 

 components showed practically undiminished precipitating activity, 

 and Vs size components showed no precipitating activity but partially 

 inhibited the reaction between the whole antigen and antibody. The 

 14 and Vs size digestion products would have molecular weights of 

 about 17,000 and 8,500 respectively. Holiday concluded that at the 

 stage of division into eight parts there is still evidence of affinity be- 

 tween the digestion products and antibody. In this connection it is 

 interesting to observe that non-protein products formed by peptic diges- 

 tion of ovalbumin, according to Tiselius and Ericksson-Quensel 

 (1939) had an average molecular weight of 1,080 (see also Haugaard 

 and Roberts, 1942). Winnick (1944) reported that partial hydrolysis 

 products from the action on casein of chymotrypsin, trypsin, pepsin, 

 ficin or papain yielded products with an average molecular weight 

 ranging from 600 to 450. Serological activities of these products were 

 not studied. 



The above facts concerning the structural specificities of polypeptide 

 molecules of as low a molecular weight as 600 to 1 ,000 seem to show 



