524 ANNALS NEW YORK ACADEMY OF SCIENCES 



22.5y/gm. of tissue. If conditions of maximal substrate concentration 

 are assumed to exist, 0.225 seconds would be required to split the 

 acetylcholine. If the assumption is made, that lower substrate concen- 

 trations exist, then a longer period would be required. Brown and 

 Feldberg also found that O.ly acetylcholine was liberated from a gang- 

 lion weighing 12.9 mg. and perfused with eserinized Lockes' solution, 

 during the first 5 minutes of preganglionic stimulation at 17 per second. 

 According to Glick, if the substrate concentration were maximal, 78 

 milliseconds would be necessary to hydrolyze this amount, or 1.5 milli- 

 seconds for splitting the acetylcholine liberated by one nerve impulse. 

 These times will be longer, if lower substrate and enzyme concentra- 

 tions are assumed. The time for hydrolysis, at the minimum rate, 

 was 8 seconds, and localization of enzyme and substrate within the 

 ganglion cell would have to be assumed, to explain enzymatic destruc- 

 tion of acetylcholine liberated by nerve impulses within the span of the 

 refractory period of 2 milliseconds. 



EFFECT OF pH AND ELECTROLYTES ON 

 CHOLINESTERASE ACTIVITY 



The effect of pH on enzyme activity is, of course, well known. Bern- 

 heim & Bernheim,'^ employing a pharmacological procedure, found a 

 pH optimum of 8.4 for the serum and brain cholinesterases of some 

 lower animals. Glick'-'' ^^ found practically this same value, 8.4 to 

 8.5 for the cholinesterases of human serum, pig's gastric mucosa, horse 

 serum, and cat brain. Calculations from the shape of the pH activity 

 curve, for these various cholinesterases, show that the activity at 7.4 

 is about 65 to 70 per cent that of the activity at optimal pH. A some- 

 what lower optimal pH, 7.5-8.0, has been reported for red cell cholin- 

 csterase." 



The effect of various ions on the activity of cholinesterase has been 

 studied by several groups of investigators. The activating effect of 

 Ca"'"' and Mg"''" is well established and, except perhaps for the magni- 

 tudes of the degree of activation, appears independent of the source of 

 the enzyme. Thus, Nachmansohn^-' found that 4 X 10"^ M Ca"""" in- 

 creased the activity of dialyzcd Torpedo electric organ cholinesterase 

 5-fold, and 4 X 10"^ Mg"'^ increased the activity about 8- to 9-fold. 

 Massart and Du Fait-" found' that horse serum, which lost 40 per cent 

 of its cholinesterase activity, on dialysis, regained its normal activity 

 in the presence of 2 X 10-' M Mg++ or Ca++. Mn++ has been found to 

 activate considerably both dialyzed Torpedo electric organ cholin- 



