160 IMMUNO-CATALYSIS 



antigen-antibody unions from investigations upon the nature of enzyme 

 reactions. Discussing the above cited resuhs of Northrop with a view as 

 to the relation of such findings to the toxin-antitoxin reaction he made 

 the following statement: "These experiments of Northrop do not, of 

 course, solve the question of antigen-antibody unions, but they do 

 serve to bring the analogy of toxin-antitoxin relations much closer to 

 laws governing the union of enzyme with substrate. Moreover, they 

 show that enzyme is actually used up in its reactions, just as toxin is 

 used up in its reactions with antitoxin, and that equilibrium follow- 

 ing the mass action law may be a definite factor in the quantitative rela- 

 tions governing the reactions. It is not at all impossible that the general 

 laws which govern reactions between trypsin and its inhibiting sub- 

 stances are similar to those which govern the toxin-antitoxin reaction. 

 Moreover, while it is a dangerous subject upon which to theorize, it is 

 yet not utterly impossible that the toxins are closely analogous to 

 enzymes, and that they produce in their action upon cells products 

 of injury which, passing into the circulation, become the specific 

 inhibitors of the toxin or the antitoxin. We do not wish to dignify this 

 with the label of a theory, but in subjects as vague as the origin and 

 biological meaning of antitoxins, we must grasp at every straw that 

 may suggest experimental paths for enlightenment." 



Since Zinsser expressed the above view two decades ago our knowl- 

 edge of the mechanism of enzyme and immune reactions has greatly 

 advanced. Numerous enzymes have been isolated in crystalline and 

 highly pure form, and their chemical nature has been clarified. With 

 the same pace the chemical nature of whole antigens, haptens and 

 antibodies has been quite extensively studied. The reactions of antigen 

 and antibody, principally through the studies of Heidelberger and 

 Kendall, have been quantitated and related to the mass action law. 

 Reevaluation and correlation of these findings appear to lend support 

 to the view expressed by Zinsser and define the nature of the analogy 

 between immune and enzyme reactions observed long ago by Ehrlich. 



B. THE FORMATION OF SPECIFIC INHIBITORS IN 

 ENZYME REACTIONS 



As stated above, by the action of an enzyme on a substrate specific 

 inhibitors, structurally related to the substrate, are generally pro- 



