38 IMMUNO-CATALYSIS 



of chemistry. Before we proceed to the elaboration and discussion of 

 other aspects of this problem, we must also discuss the question of 

 whether or not enzymes are antigenic. For the production of a specific 

 antibody in response to an antigen acting as a directive specific catalyst 

 and the antigenicity of an enzyme of which the apparent function is 

 to catalyze biological processes specifically, are intimately related. 



e. Enzymes as Antigens. It is a generally accepted fact that the 

 antigenic property of a substance, or more specifically, the production 

 of antibody against an antigen is usually dependent on the protein 

 molecule. It is also an accepted fact that the enzymic activity of a 

 substance of biological origin is dependent on the presence of protein 

 in the enzyme molecule. Even in those enzymes the specificity of 

 which is associated with a prosthetic group, this group must necessar- 

 ily be conjugated with a specific protein molecule or a "Kolloidal- 

 trager" of protein nature. In its absence the prosthetic group is 

 enzymically inactive. Likewise, when an antigen is conjugated with 

 a non-protein group, such as atoxyl, the antigenicity is conditioned 

 by the protein molecule, even though the prosthetic group may be 

 the factor determinant of serological specificity. 



From the standpoint of chemical composition, both antigen and 

 the enzyme proteins are of the same nature. Generally speaking, their 

 amino-acid content, physical properties, molecular size and their 

 behavior to various chemical treatments are of the same nature, or 

 order of magnitude. There is no theoretical basis, therefore, to exclude 

 the enzyme proteins from the family of antigenic proteins. 



The antigenicity of an enzyme protein can be determined by the 

 well known serological methods: (a) by antigen-antibody reaction in 

 vitro causing the formation of a precipitate, (b) by anaphylactic 

 tests, and (c) by inhibition of the enzymic activity as a consequence 

 of the combination between the enzyme and its specific antibody. 

 Undoubtedly, other methods supplementary to one or the other 

 method can also be employed. Of the methods the first and second will 

 be discussed here briefly, and the third will be reserved for a later dis- 

 cussion when we come to the correlative treatment of the biological 

 significance of antibodies against antigens (enzymes). 



In characterizing the antigenicity of an enzyme only by the pre- 

 cipitation method, we must be aware of the fact that every enzyme 

 preparation cannot be accepted as free of other protein impurities. 



