VELOCITY OF REACTION 81 



the substratum, so it must be supposed that some such relation- 

 ship is necessary with the reaction products, or one of them, in 

 order that the reaction may proceed in the opposite direction 

 from right to left. Nor is it any objection to the view that 

 slowing by the products of reaction is due to the tendency to the 

 establishment of the reverse reaction, that such slowing is caused 

 by one only of these products in each case ; but rather the con- 

 trary, for the enzyme in whichever direction the reaction is going 

 will probably act upon one of the cleavage products only, and 

 dependently upon the relative concentrations, either attach it to 

 the other cleavage product or detach it from it. But while there 

 is nothing in the formation of chemical compounds between the 

 ferment and either the substratum or one of its cleavage products 

 to negative the view that the retardation caused by the products 

 is anything else than the expression of a tendency to reversion ; 

 it must be pointed out that the formation of such chemical com- 

 pounds is a hypothesis invented ad hoc to explain the retardation, 

 and that there is no experiment as proof of the existence of such 

 compounds. 



That the enzyme enters into some relationship with the sub- 

 stratum, as a result of which the velocity of reaction is established 

 or increased, is certain ; and it is equally certain that the enzyme 

 also enters into some relationship at a later stage in the reaction 

 with one of the products of the reaction, as a result of which the 

 reaction is slowed. Or, when a position is considered beyond the 

 equilibrium point, as a result of which the action is made to 

 proceed in the opposite direction. But it is by no means certain 

 that this relationship is that of a chemical compound in the 

 ordinary sense of the word ; there have no such compounds been 

 isolated, there is no exact relationship pointing to any chemical 

 combination between enzyme and substratum, and the amount 

 of enzyme compared to that of the substratum which it can act 

 upon at the same instant or in an exceedingly short time interval 

 is such as to preclude in all probability the existence of a chemical 

 compound in the ordinary sense of the term. 



It is hence most probable that the influence of the enzyme 

 as an energy-transformer is one of a physical character, and at 

 any rate the formation of chemical compounds must at present 

 be taken as unproven. Accordingly it is much safer to make use 

 of a point of view which leaves the question open, and to regard 



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