SPECIFICITY IN CHOLINESTERASE REACTIONS 181 



ANIONIC SITE ESTERATIC SITE 



.|^ \ PROTEIN 



CH3-^N — CH2— CH2 



I 

 CH3 



Fig. 4 



mansohn, 1950) is an acid base catalysis. We have left out the anionic site 

 and only 



consider the hydrolytic site, the esteratic site. We have first a complex between 

 the ester and the esteratic site and we imagine an electronic cycle as indicated 

 and in which the acidic hydrogen starts moving over to the ether oxygen, with, 

 perhaps, the intermediate formation of a hydrogen bond. Finally, the alcohol 

 is split out and what is left you will recognize as a resonance form of an acy- 

 lated enzyme. 



Next, the acetyl enzyme reacts with water and forms again a complex but 

 this time an acetic acid enzyme complex. This complex dissociates to yield the 

 free enzyme and acetic acid. 



I cannot go into this at length but we have, I think, very good evidence for 

 this theory. The algebra of this two step process is as follows (Wilson and 

 Cabib (1956)). ES' is the acetyl enzyme. 



EH + S \ — ^^ EHS ^' ' ES' + ROH 



ES' + H2O ^' > EH + CH3COOH 



kE'S V^S 



V = 



(k./h + h/h)/{\ + h/h) + S Km' + S 



