ANTIBODY AS A SPECIFIC ENZYME INHIBITOR 155 



similarity between the specificity of these antigen-antibody reactions 

 and that of the action of these enzymes on their specific substrates. 

 This excellent analogy would have served as a basis for a clearer un- 

 derstanding of the immune reactions if it were at all possible to com- 

 pare antibodies to enzymes and antigens to substrates. As v\dll be dis- 

 cussed below this apparent similarity, or the analogy recognized long 

 ago, would appear to have been based on a faulty interpretation of 

 facts. At this point it suffices to state that the active groups in the 

 above antigens can function, either as a directive force in catalyzing 

 the synthesis of the specific antibodies, or as a specific point of attack 

 by enzymes, i.e., hydrolysis of a-glucoside by a-glucosidase, etc. From 

 the standpoint of antigenic specificity (and of enzyme action) of these 

 groups it is the first function, and not the second, which is of critical 

 importance. 



In a recent article Marrack (1938a) discussed the subject of "Im- 

 munochemistry and Its Relation to Enzymes." Another paper dealing 

 with this subject in a less specific manner was written by Westphal 

 (1940). From the standpoint of subject matter the paper by Marrack 

 vdll be considered here. Since the point of view with which Marrack 

 discusses this subject has a direct bearing on the validity of his con- 

 clusions, we feel justified in presenting his views in some length by 

 introducing the following quotations from his article: 



"It would be better if it were possible to study the effects of variations 

 of the chemical structure of both partners in enzyme reactions and 

 immunity reactions on the affinity between them. However, in each 

 case only one partner— the substrate in an enzyme reaction and antigen 

 in an immunity reaction— can be varied as we wish; in general we have 

 to take enzymes as they occur naturally, and antibodies as they are 

 formed in response to our injections. We are left to infer that the 

 S'pecificity of antibody and enzyme is determined hy details of chemical 

 structure to some extent comparahle to those that determine the speci- 

 ficity of antigen and substrate.'^ When we compare antigen and 

 substrate in respect of the relation of their specificity to their chemical 

 structure it does not mean that antigen and substrate are analogous 

 partners in the two paired reactions; probably antigen would be better 

 compared with enzyme. It is merely that in these two partners it is 

 possible to vary the chemical composition," and further: "Hitherto we 



* "Italics" by M. G. Sevag. 



