BOD AN SKY: CHOLIN ESTERASE 541 



cholinesterase as a "pseudo"-cholinesterase. Yet, these authors had 

 classified it as a "true" cholinesterase, since its hydrolysis of acetyl- 

 choline was inhibited by physostigmine, whereas the hydrolysis of non- 

 choline esters was unaffected by this compound. 



According to Mendel's and Rudney's criteria, the red cells of sev- 

 eral species (human, horse, sheep, ox) contained two enzymes: a spe- 

 cific or "true" cholinesterase and a non-choline ester-splitting enzyme. 

 Mendel and Rudney classified red cell cholinesterase as "true" cholin- 

 esterase, because a purified preparation hydrolyzed acetylcholine, but 

 failed to hydrolyze non-choline esters, as exemplified by methylbuty- 

 rate or tributyrin. We have found that such a purified preparation 

 splits triacetin, a non-choline ester, which Mendel and Rudney did not 

 test. ■ 



Nachmansohn and Rothenberg" have inclined towards the view that 

 specificity is relative, and that tissue extracts containing the specific 

 cholinesterase split acetylcholine at a higher rate than other esters. 

 According to these investigators, the esterase in all nerve tissue is either 

 exclusively or predominantly cholinesterase. Results which we have 

 obtained confirm those of Nachmansohn and Rothenberg, except for 

 the ester (triacetin) , which was not tested by these investigators. This 

 ester was hydrolyzed more rapidly than acetylcholine. 



The results on several aspects of the action and inhibition of various 

 cholinesterases have been summarized in table 10. Although the data 

 are not complete, it may be seen that, except in two respects, the cholin- 

 esterases may be divided into two general groups. In the first group, 

 the enzymes follow the Michaelis-Menten formulation for the relation- 

 ship between reaction velocity and substrate concentrations. There is 

 no inhibition by caffeine ; a marked inhibition by percaine ; no activa- 

 tion by Na"" and K+; and failure to hydrolyze acetyl-B-methyl cho- 

 line. In the second group, inhibition occurs at higher substrate con- 

 centrations; there are also: inhibition by caffeine; slight inhibition by 

 percaine; activation by Na"" and K""; and the ability to hydrolyze acetyl- 

 B-methyl chohne. However, as already pointed out, DFP inhibits the 

 non-choline ester hydrolysis of the enzymes, in both of these groups. 

 Although DFP seems to inhibit the cholinesterases of the first group 

 more markedly, there is considerable variation in sensitivity to inhibi- 

 tion. Moreover, there is no sharp distinction between the enzymes of 

 these two groups, with respect to the ratio of velocities at which they 

 hydrolyze triacetin and acetylcholine. This latter finding may be ex- 

 plained by assuming that there are varying amounts of non-acetyL: 

 choline hydro lyzing esterases in these preparations. Y\\ri\\QYJff^^% f q 



