50 VELOCITY OF REACTION, AND 



The analogy between chemical energy transformations and 

 those of other forms of energy is so clear and the action is so 

 obviously 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 per- 

 formance 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 trans- 

 formations it induces, but in all cases the action of such enzymes 

 is adapted, controlled, 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 

 influenced 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 



