110 IMMUNO-CATALYSIS 



enzymes, and in the latter instances with antigens and antibodies, 

 we are observing reactions with superficial groups and not deep seated 

 chemical changes in the structure of protein molecules. In immunologic 

 respects, the case of trypsinogen and trypsin, or chymotrypsinogen 

 and chymotrypsin, does not appear to deviate from the above basic 

 processes, 



b. Derivatives of Chymotrypsin and Their Properties. In a com- 

 prehensive investigation, Jacobson (1947) reported that the tryptic 

 activation of chymotrypsinogen at 0°C consists of the following trans- 

 formations: 



trypsin 



CO Chymotrypsinogen > Tr-Chymotrypsin; one peptide bond is 



(minute amounts) split. 



(a) trypsin 



■^ 8-Chymotrypsin; one peptide bond is split. 



(2) TT-Chymotrypsin 



simultaneous 

 competitive 

 , reactions 



(b) spontaneous 



> a-Chymotrypsin; three peptide bonds are 



(or autolytic) split. 



Note: In connection with the above spontaneous conversion of 

 TT-chymotrypsin to a-chymotrypsin it may be recalled that Kunitz and 

 Northrop (1935) had found that chymotrypsinogen spontaneously 

 (without the minute amounts of trypsin) undergoes a change, leading 

 to the formation of chymotrypsin. There was no marked pH optimum 

 for this change, but it occurred faster in weakly acid or alkaline solu- 

 tions independent of the effect of trypsin. 



TT-Chymotryfsin is an hitherto unrecognized chymotrypsin, and is not 

 isolated. 



B-Chymotrypsin is likewise unrecognized hitherto and is not crystal- 

 lized. Specific activities: Jacobson reported that the specific activity of 



TT-Chymotrypsin is 2 to 2.5 fold > a-chymotrypsin, and that of 8-chymo- 

 trypsin is 1.5 fold > a-chymotrypsin. 



It is most interesting to note that in the conversion of inactive chy- 

 motrypsinogen into the above three chymotrypsins, the splitting of one 

 "peptide bond" yields the most active enzyme, 7r-chymotrypsin, and 

 that a-chymotrypsin, resulting from the splitting of five (?) "peptide 

 bonds" in chymotrypsinogen, is the least active form. 



