182 



I. B. WILSON 



where 



- = A + - 



We have two successive processes that change the meaning of the ISIichaelis- 

 Menten constant. That, I think, is the trouble with the Michaelis-AIenten 

 constant. Its meaning is highly susceptible to the particular model you pick. 



For example, I have not included any pH terms but according to the model 

 we have picked and Dr. Alberty has indicated, there are also pH terms in this 

 constant. 



I would now just like to indicate what kind of Arrhenius plot could be 

 expected in a two-step process. The logarithm of the rate constant is plotted 

 as a function of the reciprocal temperature. Suppose that each step follows the 

 Arrhenius law (Fig. 5). 



The question is: What type of curve would we expect? It is clear that we are 

 going to measure something smaller than the slower step. Only if one rate is 

 much larger than the other, will we get a straight line. 



We have made a series of substrates based on the structure of acetylcholine, 

 the purpose of which was to try to find out something about the specificity in 

 kz . We have talked about specificity in binding and now we come to the ques- 

 tion of specificity in the hydrolytic process. 



(ogk 



measured 

 rate 



T 



-I 



Fig. 5 



