THE NATURE OF ENZYME ACTION 285 



start with ethyl acetate in water, for a moment the reaction 

 between ethyl alcohol and acetic acid will be absent, but as soon 

 as traces of these bodies are formed by splitting of the ester the 

 opposite reaction will commence, although at first slowly. 



Now the hydrolysis of ethyl acetate is accelerated by the 

 presence of various catalysts, such as acid(H + ions), and the 

 enzyme lipase. Is the opposite (synthetic) reaction also acceler- 

 ated by these bodies ? 



Since the equilibrium position is given by the equality of 

 the two opposite velocities, it is plain that if one only of these 

 is changed the equilibrium position must alter. So that, if it 

 is found experimentally that catalysts do not affect the final 

 equilibrium position, it follows that both the opposite reactions 

 must be correspondingly changed. 



If the view taken in the introductory remarks as to the 

 action of catalysts is correct, and that no energy is added or 

 taken away from a reacting system by the presence therein of 

 a catalyst, it would seem, a priori, necessary that the position 

 of equilibrium should be unaffected. There is, moreover, 

 direct evidence that such is the case. The question has been 

 thoroughly investigated in Ostwald's laboratory by Koelichen 

 in the case of this polymerisation of acetone by bases, and by 

 Turbaba in that of the equilibrium between aldehyde and par- 

 aldehyde. It was found in both cases that the equilibrium 

 position was unaffected by catalysts. Naturally the time taken 

 to attain thereto varied considerably, according to the catalyst 

 used. 



Many cases are known where a catalyst which accelerates a 

 particular reaction also accelerates the opposite one, when 

 acting on the products of the former. The instance already 

 given of ethyl acetate is one of these ; hydrochloric acid not 

 only accelerates the hydrolysis of the ester, but also its forma- 

 tion when acting on a mixture of acetic acid and alcohol. 



But the problem which concerns us here is, do the colloidal 

 organic catalysts, the enzymes, fall into line with the simpler 

 inorganic ones in this respect ? Practically this resolves itself 

 into this question, does an enzyme under one set of con- 

 ditions accelerate a particular reaction and under another set 

 of conditions accelerate the opposite reaction? Does lipase, 

 for example, behave like hydrochloric acid in the case just 

 mentioned ? 



