82 D. NACHMANSOHN VOL. 4 (1950) 



acetylcholine-esterase over a wide range, varying from 0.5 to 22 volts per cm^i. No other 

 enzyme tested shows any parallelism. The result supports the assumption of a close 

 relation and interdependence between these electrical and chemical processes. 



Using the same material, it has been shown that the energy released by the break- 

 down of phosphocreatine is adequate to account for the total electrical energy released 

 by the action potential. It appears probable that phosphocreatine acts, as in muscle, 

 only as a reserve for energy rich phosphate and that the breakdown of adenosine tri- 

 phosphate (ATP) precedes that of phosphocreatine. In contrast to muscular contraction, 

 however, it appears for many reasons unlikely that ATP may be the primary reaction 

 associated with conduction ^3. 24 jf ^^q postulate that acetylcholine may be directly 

 associated with conduction is correct, the hydrolysis of the ester should precede the 

 breakdown of ATP and the energy released by the latter used for the synthesis of acetyl- 

 choline. In accordance with this postulate, an enzyme, choline acetylase, was extracted 

 from brain which in cell free solution synthesizes acetylcholine using the energy of 

 ^jp32, 33 It Y^ras the first demonstration that acetylation, occurring so frequently in 

 intermediate metabolism, requires ATP energy and, more generally, that ATP energy 

 may be used outside the glycolytic cycle, in which its crucial role had been shown, first 

 by Meyerhof and his associates and later extended by the work of Parnas, the Coris, 

 Needham, Szent-Gyorgyi and many others. 



Finally it has been shown with a great variety of conducting tissues, nerve and 

 muscle, that inactivation of acetylcholine-esterase by specific inhibitors results in an 

 abolition of conduction^'' ^4 jj^jg effect is easily reversible with compounds which 

 inhibit the enzyme reversibly. With DFP, an inhibitor which inactivates the enzyme 

 irreversibly, the abolition of conduction becomes irreversible. However, the irreversible 

 inactivation of the enzyme is a relatively slow process. Its rate depends on a great 

 number of factors^^. Therefore, this compound was particularly suitable for testing the 

 essentiality of acetylcholine in conduction. A striking parallelism has been established 

 in nerves exposed to DFP between the progressive inactivation of acetylcholine-esterase 

 and the abolition of conduction as a function of time and temperature. In no way is it 

 possible to dissociate conduction from acetylcholine-esterase activity^^' ". Claims to the 

 contrary were shown to be due to the use of inadequate techniques. The minimum 

 amount of enzyme required for unimpaired conduction is relatively small, about 10% 

 of the total activity present. Considering the smallness of the initial heat, the remaining 

 activity is, however, still adequate^. The excess is not unusual and is in* accordance 

 with the experience with other enzymes, but it led to some misinterpretations in the 

 early phase of the investigations. 



The view that the acetylcholine-esterase system is essential in conduction appears to 

 be well established. The precise function of the ester is, however, unknown. It is possible 

 that, during activity, a higher rate of collision of sodium or potassium ions with the ace- 

 tylcholine-protein or lipoprotein complex leads to a release of the ester. This process may 

 be an essential factor in the alterations of the membrane proteins leading to an increased 

 permeability. The possibility of a rapid removal of the active ester by acetylcholine- 

 esterase which would restore the resting condition permits such an assumption. No other 

 process is known to have the necessary speed. An electrogen'c action of the ester may be 

 demonstrated in electric tissue, as will be discussed later. In connection w'th the great 

 number of other electrical and chemical observations the hypothesis appeals worthy of 

 consideration. In this connection, the experiments reported in the following paper on 

 References p. 93 195 ■ 



