522 ANNALS NEW YORK ACADEMY OF SCIENCES 



centration, and Kg is the dissociation constant of the intermediate 

 enzyme-substrate complex. 



The second type of relation obtaining among some cholinesterases 

 appears to be one in which inhibition of reaction velocity occurs at 

 higher substrate concentrations. This relation has been found to hold 

 for some other enzymes, such as lipases, catalase, oxygenase.* The 

 reactions between substrate and enzyme may be formulated as follows: 

 E + S ?^ ES (active) 



ES + (71 - l)S:f± ESn (inactive) 



ES ^E + P. 



The relation between substrate and reaction velocity has been devel- 

 oped by Haldane^ for the reaction where n = 2, as follows: 



' max *-' 



V = 



S" 

 S + A% + ^ 



A2 



(2) 



where K2 is the dissociation constant of the inactive enzyme-substrate 



r p on r oin— i 



compound - — rlF^^ — When the velocity is plotted against the log- 



[Ebn\ 



arithm of the substrate concentration, a bell-shaped curve is obtained. 

 The values for K,, Ko may be obtained by transformation of the 

 above equations, according to the method of Lineweaver and Burk.* 

 Since there are very few and incomplete data in the literature for 

 cholinesterases which follow this type of substrate-reaction velocity 

 relationship, we shall not attempt such an evaluation. 



In TABLE 1, are listed the results of investigations on the relationship 

 between concentration of the substrate, acetylcholine, and the velocity 

 of cholinesterase action. It may be seen that the chohnesterases 

 present in human and dog serum, and in the cat superior cervical gang- 

 lion, show increasing rates of reaction, with increasing substrate con- 

 centrations, which become asymptotic to a maximal rate at infinite 

 substrate concentration. These values of the dissociation constants 

 (molar concentration at which one-half maximal reaction velocity oc- 

 curs) range, in general, from 1 to 1.7 X 10"^ In contrast, the cholin- 

 esterases from the red cells of man, sheep, horse, and ox, and from the 

 brain of the mouse and dog, do not show increasing reaction velocities 

 with increasing substrate concentration. According to Mendel and 

 Rudney," and to Alles and Hawes,'' they show optimal activity at 

 about 1 X 10-^M; at concentrations higher than this, the reaction 

 velocities decrease. 



On the other hand, values for the optimal concentration obtained by 

 Zeller and Bissegger,^^ and by Nachmansohn and Rothenberg," are 



