1 44 IMMUNO-CATALYSIS 



find their answer in the concept as to what constitutes an enzyme. If 

 we confine the term enzyme to certain famiHar substances of biological 

 origin capable of catalytically breaking down in vitro or in vivo certain 

 selected substances, or capable of synthesizing higher complexes out of 

 simple substrates, we will be setting artificial barriers or placing the 

 known enzymes as an exclusive class behind closed bars. If on the 

 other hand, we define an enzyme (or an antigen) as any protein 

 capable of performing a specialized physiological function in accord- 

 ance with the well known criteria of ideal catalysis, a comprehensive 

 theory of biocatalysis is provided which links antigens, enzymes, vita- 

 mins and hormones* and possibly other still unknown substances of 

 similar role. The knowledge gained from the study of one family of 

 biocatalysts will be useful in elucidating the mechanism of certain un- 

 explained processes associated with other biocatalysts. 



A. NATURE OF THE ANALOGY BETWEEN IMMUNE AND 

 ENZYME REACTIONS 



For over half a century immunologists have observed an analogy 

 between immune and enzyme reactions. This analogy has been based 

 on the fact that immune bodies react with antigens or their parts 

 (haptens) with a high degree of specificity which favorably compares 

 with the specificity exhibited between enzymes and their substrates. 



The origin of the above cited analogy between immune and enzyme 

 reactions goes back to as early as 1890. During this period notable ad- 

 vances were made in the study of the specificity of immune reactions, 

 chemistry of proteins, carbohydrates, and the enzyme reactions by Emil 

 Fischer, Behring, Ehrlich, Bordet, Calmette, Kitasato and many other 

 investigators. In 1890 Behring discovered that the serum of an animal 

 immunized against diphtheria was capable, when injected into a fresh 

 animal, of conferring immunity upon the latter, which, failing the use 



to the preexistence of other proteinases. There is, in Hfe, a practically endless sequence 

 of sequence reactions, in which one proteinase synthesizes the next by a predetermined 

 reaction, and so forth. The sequence breaks off whenever a proteinase has sjTithesized 

 a protein that does not possess enzymatic properties." 



The definition, as suggested by us, embracing the versatile properties of the protein 

 molecule is not in strict agreement with the implications suggested by the last sentence 

 of the above quotation from Bergmann. 



*The reader is referred to an excellent review on the studies of the antigenic 

 properties of hormones by Thompson (1941). 



