ACTION OF ENZYMES 51 



point. For if the equilibrium point differed in the presence and 

 absence of the enzyme, then by working a cycle with the catalyst 

 in the solution, then removing the catalyst and excess products 

 of activity, and replacing the catalyst again, energy could be 

 continually manufactured from nothing, or working in the opposite 

 direction energy could be destroyed ; both which results are 

 obviously contrary to the law of conservation of energy. 



To this reasoning the following objections may be taken : 



1. The assumption is wrong that because the catalyst is not 

 permanently altered in the process it cannot therefore take up 

 or give out energy to the system, because it excludes (a) the 

 possibility of the catalyst operating upon external energy, which 

 is done, for example, by the chlorophyll-bearing cell ; (b) the 

 possibility of the catalyst using part of the chemical energy of the 

 system, to run another reaction in which energy is absorbed, as 

 is done by all living cells. 



2. Even for catalysts in the restricted sense, there is nothing 

 in the reasoning to show that the catalyst cannot take up and 

 give out energy in a vibratile fashion, so that as a net result its 

 own condition and amount of energy is unaltered, and its condition 

 at the end is the same as at the beginning, and yet by this means 

 it can induce a reaction which would not occur at all in its absence. 

 For example, an electro-motor is not altered at the end of a period 

 of running from what it was at the beginning, but by intermedi- 

 ately taking up an amount of energy it is capable of converting 

 a large amount of electrical energy into mechanical energy which 

 would never have occurred if it had not been in the electric circuit. 

 So when a chemical reaction is absolutely stationary on account 

 of opposed molecular attractions present in the molecule having 

 a tendency to react, the enzyme by imparting momentarily a 

 small amount of energy to the molecule may overcome the mole- 

 cular attractions, and in the break up of the molecule may receive 

 back all the energy previously given out, so as to remain un- 

 changed in the process. 



Finally, as has been pointed out above, the presence of the 

 catalyst may not cause the reaction to proceed completely to 

 the equilibrium point, because as the reaction proceeds, and the 

 concentration of the substance reacting changes, the potential 

 tendency backing the action of the catalyst may fall to 

 such a level that the energy in the first stage which the catalyst 



