ENZYMES 39 



which otherwise would not do so. The catalyst will, as 

 a rule, influence a reaction between amounts of reagents 

 many thousand times its own weight, and it can generally 

 be recovered unchanged in quantity and constitution at 

 the end of the reaction. 



Enzymes are not only catalytic in their action but 

 are often much more active than inorganic catalysts 

 which bring about the same reaction. The enzyme 

 lactase, for example, hydrolyses the disaccharide, lactose, 

 to glucose and galactose many hundreds of times more 

 rapidly than does twice normal hydrochloric acid where 

 the hydrogen ions act as the catalyst. Inorganic catalysts, 

 such as acid in the instance just described or in the hydro - 

 l^^sis of esters, 



CHgCCOC^Hs + H2O ^==^ CH3COOH + C0H5OH, 



do not alter the equilibrium point of the reactions which 

 they catalyse but only shorten the time required to 

 attain the equilibrium condition. That is, the catalyst 

 accelerates both directions of a reversible reaction to an 

 equal extent. Likewise the amount of catalyst has no 

 influence on the final equilibrium quantities of the 

 reagents, but the velocity with which the equilibrium 

 state is reached is proportional to the amount of catalyst. 

 Under strictly controlled conditions this is also generally 

 true of enzymes, although in certain cases enzjnnes may 

 alter the equilibrium value as well as the velocity of a 

 reaction. This is in all probability due to their colloidal 

 nature and a complete irreversible adsorption of a part 

 of the reactants, with consequent alteration of the active 

 concentrations on which the equilibrium depends. During 

 a reaction enzymes often become partially destroyed or 

 lose some of their activity as a result of side reactions, 

 with a consequent slowing down of the velocity of the 

 reaction, although the final equilibrium reached is un- 

 altered. 



