MECHANISM OF ANTIBODY FORMATION 109 



action from another protein. Ten Broeck (1934) reported that guinea 

 pigs receiving chymotrypsinogen were sensitized against the so-called 

 precursor itself but not against chymo trypsin, and guinea pigs receiving 

 chymotrypsin were sensitized against itself, but not against chymotryp- 

 sinogen. But, he also reported that in some cases there were cross- 

 reactions, particularly between the chymotrypsin and chymotryp- 

 sinogen, indicating a close serological relationship between the inactive 

 and active proteins. 



In the absence of minute amounts of trypsin, the change from 

 chymotrypsinogen to chymotrypsin may occur spontaneously, slowly at 

 pH 5.0, and faster in slightly acid or weakly alkaline solutions. The 

 change from trypsinogen to trypsin is reported to occur in the presence 

 of calcium ion and at pH 7.0 to 9.0 without the aid of any outside 

 activator. Under these conditions, the increase of five free amino groups 

 in chymotrypsin does not appear to indicate an opening up of stable 

 peptide linkages as would result from the characteristic action of 

 proteolytic enzymes. These changes may involve salt-like reactions with 

 basic or acidic groups, or result perhaps from a reaction involving 

 hydrogen bonding. Under such conditions a serological difference 

 between the two forms of protein is conceivable (see Pauling in Land- 

 steiner, 1945). As such, chymotrypsinogen, for example, could be a 

 derivative of chymotrypsin and not a precursor. In relation to this, it 

 may be pointed out that an antigen can be modified in similar manner 

 to yield an immunologically different protein derivative. Landsteiner, 

 et al. (1932) reported a serological difference between an antigen 

 with a terminal -COOH group and that having -CONH2 as terminal 

 group instead. Or immune sera prepared with a methyl ester antigen 

 precipitated the homologous azoprotein but not that made from the 

 parent, p-aminobenzoic acid. If the ester was hydrolyzed by gentle 

 alkaline treatment of the azoprotein a strong reaction with serum for 

 p-aminobenzoic antigen (Landsteiner, et al. 1927) took place. Chow 

 and Goebel (1935) showed that acetylation of the amino groups of an 

 antibody abolished its reactivity with a specific polysaccharide. Con- 

 versely, the esterification of the -COOH group of the polysaccharide 

 deprived it of its reactivity with the native antibody. Saponification of 

 the esterified carbohydrate restored the activity to react with the 

 specific antibody. 



In the above cited instances with the inactive and active forms of 



