ANTI-ENZYME IMMUNITY 195 



of antipepsin immune serum was explained by Northrop by the fact 

 that the active pepsin injected must have been almost instantly in- 

 activated in the animal body, due to the neutral reaction of the circulat- 

 ing body fluids. For it was shown that pepsin is instandy more than 

 half inactivated at pH 6. It would therefore seem that it is almost 

 impossible to prevent the denaturation of active pepsin in the animal 

 system; antibody may be formed against the denatured enzyme. 



B. A CRITICAL CONSIDERATION OF THE ANTIGEN-ANTI- 

 BODY REACTIONS IN RELATION TO THE INHIBITION OF 

 ENZYMES BY SPECIFIC ANTIBODIES 



I. An Analysis of the Reactions of the Active Groups of 

 Proteins in Relation to their Biological Specificities 



The ability of enzyme proteins to stimulate the formation of specific 

 antibodies is now an established fact. There are, however, questions 

 pertaining to the inhibition of the enzymes by respective antibodies 

 which require consideration. The complexity of these questions and 

 the inadequacy of the available data do not permit us at present to 

 treat them satisfactorily. One can only raise questions and discuss them 

 as plausibly as possible. These questions may be formulated in the 

 following manner: 



(1 ) Are the SH, -S-S-, NH2, tyrosine, etc., groups which are studied 

 in relation with the inactivation or activation of certain enzyme pro- 

 teins the sole determinant factors? Or are the reactions involving these 

 groups simply superficial manifestations of other more significant 

 changes which the protein molecule undergoes which we have not as 

 yet been able to determine. 



(2) Do the anti-enzyme antibody molecules contain specific com- 

 bining sites elicited in response to the stimulation of the active groups 

 of enzymes? 



(3) Do the inhibitions of enzymes by homologous antibodies result 

 directly from the interaction of the respective specifically reactive 

 groups of enzymes and antibodies in a manner identical with those of 

 other antigens and antibodies? Or are these inhibitions due to second- 

 ary effects resulting from the formation of antigen-antibody complexes? 



(4) Are the inhibitions due to the mechanical blocking of the en- 



