CATALYSIS AND ENZYMES 

 FUNDAMENTAL FACTS 



SINCE the work of Berthelot and Pean de St Gilles (1862) it has been a familiar 

 fact that, if ethyl acetate and water be mixed in molecular proportions, and 

 allowed to remain for some weeks, the ester is hydrolysed with formation of 

 ethyl alcohol and water; but, however long a time be allowed to elapse, only 

 a certain part of the ester undergoes conversion, although there is sufficient water 

 to hydrplyse the whole. The rate of change becomes slower and slower until 

 it ceases, and at this time it is found that the four components of the system are 

 present in the proportion of one-third of a gram-molecule each of alcohol and 

 acid, two-thirds of a gram-molecule each of ester and water. 



Further, suppose that we have commenced with acetic acid and alcohol, 

 also in molecular proportion, and have allowed the reaction to proceed until 

 it stops, we find that we obtain the same proportion of the four components. 

 Clearly we have to deal with a case of equilibrium, or balance of opposite 

 reactions. 



Now these reactions, which for the present purpose we may regard as being 

 spontaneous, are extremely slow. We can, however, increase their rate enormously 

 by adding some mineral acid. In this case, the attainment of equilibrium, which, 

 left to itself, takes weeks, can be brought about in a few hours. There are three 

 important facts to be noticed here. FifStt^^he composition of the system 

 in equilibrium is the same under the action of acidal^vhen reached spontaneously. 

 Secondly, the acid added is found, after its work is done, still present in the same 

 state as it was originally. Lastly, whether we start from ester and water, or 

 acid and alcohol, we find that the rate of the reaction is accelerated by the 

 addition of acid. This latter fact follows, as we shall see later, from the other 

 fact that the equilibrium position is not changed by the presence of the acid. 



Let us take now, instead of acid, an extract of the pancreas and, in place of 

 ethyl acetate, another similar ester, amyl butyrate. 



The experiment was made by Dietz (1907) and the higher ester was used for convenience in 

 calculating the results, since the spontaneous reaction is so slow as to be undetectable during 

 the time of the experiment ; in other respects, the system may be regarded as precisely similar 

 to the previous one. 



The effect of the pancreatic extract is even more powerful than that of acid 

 in accelerating the reaction. Otherwise, the three facts to which attention was 

 called in that case are also to be noticed in this, with one slight exception, 

 namely, that the position of equilibrium is not quite the same as that under acid 

 or the spontaneous one. Fig. 4 (p. 86) in my monograph on " Enzyme Action " 

 shows that the position of equilibrium is the same when attained from either 

 direction, a fact also obvious from Fig. 80 of the present work. 



One more case will be instructive, before we proceed to discuss the meaning 

 of the facts before us. This is the one to which Fig. 81 refers. The system here 

 is one of glucose, glycerol, glycerol-glucoside, and water. The equilibrium is 

 brought about under the agency of a substance obtained from almonds, and known 

 as emulsin. The curves, taken from experiments of my own (1913, 1), show that 

 the equilibrium position is the same, whether we start from glucose and glycerol 

 or from glucoside and water. The additional fact is that we are dealing with 



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