THE SYNTHESIS OF PROTEINS 39 



It appears to the writer that this hypothesis predicts that injection 

 of an animal with antiserum should lead to the production of more anti- 

 bodies, since the production of the antibody-forming proteinase is as- 

 sumed to be autocatalytic. These proteinases are assumed to be present 

 in the blood and so should cause formation of antibody when blood con- 

 taining them is injected into a different animal. Actually the injection 

 of antiserum does not lead to the production of more antibodies, but on 

 the contrary the antibody injected disappears quite rapidly. It is possible 

 to avoid this discrepancy by means of secondary hypotheses, but it ap- 

 pears to be a serious objection to any purely autocatalytic mechanism. 

 There is no experimental evidence for the existence of the "proteinases," 

 as far as the writer is aware. In the absence of such evidence the assump- 

 tion of their existence seems unnecessary and leads to the further com- 

 plication of accounting for their own formation. 



Sevag's Hypothesis. Sevag (1945) has recently reviewed the 

 various hypotheses for the formation of antibodies and has carefully 

 and thoroughly discussed the relation of antigens to enzymes. There is 

 no doubt that many points of similarity exist between the action of 

 enzymes on their substrates and the formation of antibodies after injec- 

 tion of antigens. Sevag concludes that all proteins are enzymes and that 

 antibodies are formed as a result of the action of the antigens (enzymes) 

 on the normal globulins. According to this hypothesis antibodies should 

 be readily formed by the action of antigens on normal serum in vitro, 

 but this is not actually the case. This discrepancy, however, cannot be 

 considered conclusive owing to the difficulty of carrying out such an 

 experiment under the conditions which exist in the blood vessels. 



Sevag's hypothesis also predicts that antibodies can be produced only 

 so long as antigen is present. 



Antibody Formation from Proteinogen 



The writer agrees with Burnet that antibodies and adaptive enzymes 

 are closely related and are probably formed by the same mechanism. The 

 hypothesis describing the formation of adaptive enzymes outlined above 

 is simpler than that of Burnet and agrees as well with the known facts 

 of antibody formation. 



The reaction may be summarized as follows : 



I. The normal serum proteins are formed from the "proteinogen" 

 by an autocatalytic reaction. 



