NERVOUS ACTION 



In these extracts, the enzyme is about twice as pure as in those obtained 

 from fresh tissue — one gram of protein may form 3 to 4 mg. of acetyl- 

 choUne in one liour. 



Since acetone inactivates choline esterase, this enzyme is largely 

 or sometimes completely inactivated in the extracts prepared from 

 powder of acetone-dried brain, so that addition of eserine may have 

 either a small effect or practically none on the formation of acetyl- 

 choline. It is thus demonstrated that the enzyme mechanism re- 

 sponsible for the formation of the ester is not identical with the hy- 

 drolyzing enzyme. But this is not surprising in view of the complexity 

 of the ester synthesis, which probably occurs in several steps involving 

 more than one enzyme. Adenosine triphosphatase is also removed 

 in extracts from acetone-dried brain. No addition of fluoride is there- 

 fore required. 



The enzyme requires the presence of potassium in high con- 

 centration, close to that found in brain. It contains active sulfhydryl 

 groups which may be easily oxidized in air and which are readily in- 

 activated by monoiodoacetic acid or copper in low concentrations. 

 On dialysis, the enzyme rapidly loses its activity. Addition of glutamic 

 acid reactivates it partly. Only the naturally occurring /(+)-form 

 is effective (15). With potassium and glutamic acid, 50 to 80% of 

 the original activity may be restored. Further addition of cyanide or 

 replacement of glutamic acid by cysteine may reactivate the enzyme 

 nearly completely. /(+)-Alanine also has some effect; other amino 

 acids have either a weak effect or none. Citric acid has an effect nearly 

 as strong as glutamic acid, whereas dicarboxylic acids have practically 

 no effect. 



The effect of glutamic acid, although weaker than that of cys- 

 teine, appears to be of special interest. Cysteine, like glutathione, 

 may enhance the activity of many enzymes containing sulfhydryl groups 

 which have been oxidized during preparation, whereas the effect of 

 glutamic acid cannot be explained by action on the sulfhydryl groups 

 of the enzyme. 



Price, Waelsch, and Putnam (19) have observed a favorable 

 effect of glutamic acid on patients suffering from petit mal attacks. 

 The interest in the effect of glutamic acid on choline acetylase is, by 

 this clinical observation, further increased, since a relation between 

 the clinical effect and the enzyme reactivation is easily conceivable. 



347 



