CATALYSTS AND ENZYMES 241 



MEANS OTHER THAN CATALYSIS BY WHICH CHEMICAL REACTIONS 



CAN BE INDUCED, OR REACTION VELOCITY VARIED. 



Catalysis is not the only means by which a reaction may be 

 induced, or the resistance to a reaction be reduced. We have 

 seen that provided any energy transformer is included in the 

 resisting system whereby energy can be added to the reaction, 

 the reaction need not run towards the equilibrium point, but 

 instead the chemical energy may be increased, and complex chemical 

 substances possessing more chemical energy may be built up from 

 simple and completely oxidised inorganic substances, and we 

 have instanced the chlorophyll-containing cell of the plant as an 

 example of such an energy transformer which is capable of con- 

 verting radiant solar energy into chemical energy. In all living 

 cells we have, however, examples of such reaction in which energy 

 set free from one reaction is utilised to run another. 



To consider, accordingly, that all the reactions of cell life are 

 catalytic is to take a narrow and incomplete view of the problem 

 of the chemical life of the cell. Important to the cell economy 

 as are those reactions induced by enzymes, they form but one 

 portion of the whole, and if the chemistry of the cell included 

 only such reactions as could be induced by enzymes, there would 

 be no building up of compounds with greater chemical potential 

 such as actually occurs : the whole process would become katabolic. 



It is the linkage of one reaction with another, and the using 

 of the free energy of one to run another, which specially char- 

 acterises the cell and differentiates the cell from the enzyme. 



In such a connection of two reactions there is something there- 

 fore superadded to the action of a catalyst. The catalyst can 

 only alter the resistance to the induced reaction. An inducing 

 reaction can in addition add energy to the reaction induced because 

 it itself gives out free energy. 



Hence the old idea of Liebig, that a body which is itself in a 

 state of reaction may induce reaction in another body, although 

 not a necessary part of a theory of catalysis, because both bodies 

 are altered, must not be lost sight of, since it is of high importance 

 to chemical kinetics, and more especially for the chemistry of 

 the ceU. 



It may be noted that an induced reaction by such a body may 



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