184 



I. B. WILSON 



TABLE IV 

 Values of y^s , AH+ and AS* at 25° and pH 7 



Acetj'lcholine 



Dimethylaminoethyl acetate 

 Methylaminoeth\-l acetate . . 

 Aminoethjd acetate 



>3 



1.5-3.4 X 106 



3.3-3.5 X 105 



1 . 1 X 10« 



9.0 X 103 



AH* 



14-19 X 103 



6.7-8 

 8.0 

 9.5 



AS* 



(16-34) 



-(6.5-10.5) 



-9 



-9 



to the acetylcholine curve as indicated in the figure. These values are presented 

 in Table 4. 



The energy of activation data is interesting because acetylcholine, which is 

 the best substrate, has by far the largest energy of activation. The others do 

 not differ too much. 



When we turn to the entropies of activation as calculated from the absolute 

 rate theory formulas, we see that acetylcholine is a much better substrate than 

 the others because the entropy of activation is much more favorable than for 

 the other substrates. It appears that the interaction of a quaternary structure 

 with the anionic site promotes the catalytic activity through the entropy of 

 activation. The anionic site thus not only serves to bind the substrate and 

 thereby make A',„ small but also promotes the catalytic activity making k^ 

 large. 



There are a number of inhibitors such as tetraethylpyrophosphate and 

 diisopropyl fluorophosphate, which are called irreversible inhibitors. They 

 phosphorylate the enzyme: they phosphorylate the same grouping which is 



ANIONIC SITE 



ESTERATIC SITE 



PROTEIN 



"■■"■■"■" 



PROTEIN 



imiM 



Fig. 7 



