RECIPROCAL CATALYSIS 445 



anti-trypsin which appear in the circulation after the injection 

 of the enzymes do so as a result of the production of the synthe- 

 sizing form in restoration of the equilibrium between the synthe- 

 sizing enzyme and the hydrolysing form. 



The hypothesis which I have put forward (53) in explanation 

 of the phenomena of protein hydrolysis and synthesis is a modi- 

 fication and extension of Euler's hypothesis, and involves the 

 view that these processes are examples of which I have termed 

 " reciprocal catalysis." The essential features of this hypoth- 

 esis have already been embodied in equations (A) to (D) in Chap. 

 XV, section 1. For convenience of reference they may be recap- 

 itulated here. 



We know that during or preceding the hydrolysis of proteins 

 by proteolytic enzymes the ferment combines with the substrate 

 (previous chapter, 2). Furthermore, the reaction consists in the 

 introduction of the elements of water into COH.N bonds 

 of the protein molecule, each bond which is attacked yielding 

 two molecules. We may therefore represent the reaction of 

 hydrolysis as follows: 



HF 

 I 



(A) - COH.N - + HFFOH - - COH.N - 



I 

 FOH 



HF 



I 



(B) -COH.N -COOH + H 2 N- + FF . 



I 

 FOH 



while, subsequently, the dehydrated form of the enzyme (FF) 

 reacts with water to regenerate the hydrated form : 



(D) FF + H 2 + HFFOH 



enzymatic synthesis of a protein consisting in the reverse of 

 these reactions. 



The net result of the first two reactions is the transference of the 

 elements of water from the ferment to the substrate molecule, 

 while, in the third reaction, the ferment recoups itself from the 

 medium. Provided the station of equilibrium in the reaction 

 (D) lay far enough to the right and the velocity of this reaction 



