VOL. 4 (1950) 



ACYLATIONS BY ACETYLCHOLINE ESTERASE II 



315 



The effect of pn on the equilibrium might be interpreted as follows. On general 

 grounds, it seems reasonable to suppose that the immediate product of ester hydrolysis 

 is the undissociated acid molecule rather than its ion : 



RCOOR' + H2O ^ RCOOH + R'OH 

 RCOOH ^ RCOO- + H + 



(I) 

 (2) 



where RCOOR' represents the ester and RCOOH and R'OH the acid and alcohol products 

 of hydrolysis. Equilibrium in the synthesis will then be defined by the relationship: 



H2O] [RCOOR'] 



K = 



R'OH] [RCOOH] 



where K is the Nernst equilibrium constant calculated from concentrations in molarity. 

 As Pjj is decreased, the concentration of the undissociated acid rises and an accompanying 



120. 140 



Minutes 



Fig. 4. Synthesis of propionylcholine as a function of pjj- Solutions were made with 1.21 g of choline 



chloride and 0.85 g of sodium propionate at pn 7 and 5.8 in a total volume of 6.0 ml, and with i.oi g 



of choline chloride and 0.71 g of sodium propionate at pn 5-o in the same total volume. Temperature 



18° C. Procedure otherwise as described under Fig. 3. 



References p. 321. 



