312 



S. HESTRIN 



VOL. 4 (1950) 



TABLE II 



ACETYLCHOLINE HYDROLYSIS IN BORATE SOLUTION AS A FUNCTION OF PH IN THE ALKALINE RANGE 



a) Reaction mixtures contained a constant amount of enzyme, acetylcholine chloride 4 ^M/ml., 

 0.07% gelatin and 2 ml of Sorensen borate buffer in 4 ml of final mixture. Temperature 21° C. 

 PH remained unchanged within 0.2 pH units throughout the course of reaction. Non-enzymatic 



hydrolysis was negligible. 



b) As in a) but with borate-potassium chloride-sodium carbonate solutions of Atkins and Pantin^^ 

 as the buffer. Enzyme was added to the reaction mixtures as the last component. By use of a high 

 enzyme concentration and a rather low temperature for the incubation the relative role of the non- 

 enzymatic hydrolysis could be kept to a minimum. The same device served also to prevent undue 

 interference at highly alkaline pn by progressive inactivation of the enzyme. The temperature was 

 17° C. ph remained unchanged within 0.2 pjj units throughout the observed course of the reaction. 



hydrolysis was essentially independent of pn is relatively wide. The pn function of the 

 acetylcholine esterase from electric tissue differs in this respect from some other esterases 

 which have been studied by Glick^. 



The effect of addition of choline and acetate on acetylcholine hydrolysis has been 

 studied in detail by Augustinsson^". It seemed of interest to ascertain whether p^ 

 influences the role played by the hydrolysis products. In an experiment reported in 

 Table III the effect of choline chloride (12.5 /iM/ml) on the hydrolysis of acetylcholine 

 (4 fjMjmY) at three selected pn values is shown. Choline proved to be about equally 

 inhibiting at pjj 7-7 and 6.8; the choline was only about one-half as active an inhibitor 

 at Ph 5.9. Acetate even in high concentrations (o.i M) failed to inhibit acetylcholine 

 hydrolysis by electric tissue esterase in phosphate solution either at pn 5-5 or 7.7. Since 

 References p. 321. 



