CHOLINESTERASE 



By Oscar Bodansky* 



Medical Division, Chemical Warfare Service, Edgewood Arsenal, Maryland^ 



On the basis of his studies on the pharmacology of acetylcholine, in 

 1914, Dale stated: "In the blood at body temperatures it seems not im- 

 probable that an esterase contributes to the removal of the active 

 ester from circulation."^ In 1926, Loewi and Navratil observed that 

 acetylcholine, as well as "vagus substance," was rendered inactive by in- 

 cubation with heart extract.^ However, such inactivation did not 

 occur after the heart extract had been heated or subjected to ultra- 

 violet irradiation. These observations by Loewi and Navratil in- 

 augurated the study of the enzyme, cholinesterase. 



A heat-labile substance which is capable of hydrolyzing acetylcholine 

 is found very widely distributed in the organs and fluids of the body. 

 It cannot be assumed that, apart from this common property of hy- 

 drolyzing acetylcholine, the other properties of this enzyme are the 

 same in all these tissues. Our present discussion should most fit- 

 tingly concern itself with the properties of this enzyme as found in 

 nervous tissue, and should determine the extent to which these proper- 

 ties play a role in nerve activity. However, most of the data avail- 

 able for discussion describe chiefly the properties of cholinesterase 

 found in serum, red cells, and, to a lesser extent, in the whole brain. 

 The extent to which these data apply to the properties of cholinesterase, 

 at synapses and in other nerve tissue, should be carefully evaluated. 



RELATION BETWEEN SUBSTRATE CONCENTRATION AND 



REACTION VELOCITY 



We shall first turn our attention to the relation between the rate of 

 action of cholinesterase and the concentration of the substrate, acetyl- 

 choline. Examination of the data shows that two types of relation- 

 ships hold. The first type appears to follow the Michaelis-Menten 

 formulation:^ 



-^ = ^ (1) 



where v is the reaction velocity at substrate concentration S, F^ax 

 is the maximum reaction velocity occurring at infinite substrate con- 



* Lt. Colonel, M. C, A. U. S. 



t Present address: Dept. of Pharmacology, Cornell University Medical College, New York, N. Y. 



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