ACTION OF ENZYMES AND CELLS 171 



of the same nature, that we may summarise the action of a catalyst 

 or energy transformer as follows : 



1. The action of the soluble or unorganised catalyst or enzyme may 

 consist (a) in commencing a reaction which does not proceed at all in its 

 absence; (b) in altering the velocity of a reaction which does proceed in 

 its absence, and such action may be positive, increasing the speed of the 

 reaction, or negative, diminishing the speed of the reaction; but (c) the 

 direction of reaction must always be towards the point of equilibrium, as 

 defined in the previous section, because the enzyme does not yield energy 

 itself, and is unable to act as a transformer to external energy, or to link 

 two chemical reactions so as to obtain energy from one for the performance 

 of the other. 



2. The living cell as an energy transformer, in addition to the actions 

 (a) and (b) of the enzyme, can. store up chemical energy, either by using 

 energy in other forms and converting it into chemical energy, or by linking 

 several reactions together and transforming the chemical energy obtained 



from some back to chemical energy which is stored up in others. Finally, 

 the cell can modify its activities, and alter in its action as a transformer, 

 changing entirely the course of the reactions it induces and the products 

 obtained, while the type of action of the enzyme is simple, selective, and 

 entirely fixed. 



There is no doubt whatever that the cell makes use of the action 

 of many intracellular enzymes for the chemical transformations it 

 induces, but in all cases the action of such enzymes is adapted, con- 

 trolled, and co-ordinated by the cell. 



It is necessary to point out that the above view as to the action 

 of enzymes is different in many essential points from the one which 

 is usually accepted at the present time. 



The currently accepted view is that any reaction which is in- 

 fluenced by catalysts is already proceeding in the absence of the 

 catalyst, and that all the catalyst can do is to alter the speed of 

 reaction, and bring the reaction more quickly or slowly to that 

 equilibrium point which it would inevitably have attained in its 

 own time in the absence of the catalyst. 



The statement is based on the fact that the catalyst is not itself 

 altered in the reaction, and hence neither takes up nor gives out 

 energy to the system; accordingly it cannot alter the amount of 

 energy in the system, and must lead to the same equilibrium 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 solu- 



