NACHMANSOHN: CHEMICAL MECHANISM IN NERVES 407 



of hydrolysis of different substrates by the highly purified enzyme are 

 compared to those obtained with the homogenized suspension of electric 

 tissue, the pattern obtained remains exactly the same throughout the 

 whole process of purification (figure 4). Both have the pattern char- 

 acteristic for cholinesterase. Thus, the correlation established between 

 voltage and enzyme activity can be consequently referred to a corre- 

 lation between ACh metabolized and voltage developed. 



It may be noted that examination in the analytical ultracentrifuge in- 

 dicates that the enzyme is a very large molecule. These are not yet 

 final observations. If they could be confirmed, they would indicate 

 that the turnover number of the enzyme is many milhons per minute 

 and that one molecule of cholinesterase could split one molecule of 

 ACh within a few microseconds. 



B. The Energy Source of the Nerve Action Potential 



The second line of investigations, in which enzyme activity could be 

 correlated with events in the living cell recorded by physical methods, 

 is based on the energy transformations involved and on thermodynamic 

 considerations. 



If the release and removal of ACh are associated with the primary 

 alterations of the nerve membrane during the passage of the impulse, 

 then the primary source of the chemical energy released during the re- 

 covery process should be used for the resynthesis of ACh. 



The most readily available source of energy in living cells is that 

 released by energy-rich phosphate bonds. Phosphocreatine, the main 

 "storehouse" of energy-rich phosphate bonds in muscle, is also present 

 in nerves. The electric organ offers a suitable material for investigat- 

 ing the chemical reactions which supply the energ}^ for the action po- 

 tential. Both electric and chemical energy released are within the 

 range of measurement, whereas, in ordinary nerves, such an analysis 

 is difficult. 



Measurements carried out on the electric organ of Electrophorus 

 electricus have revealed that the chemical energy released by the break- 

 down of phosphocreatine is adequate to account for the electric energy 

 released by the action potential. The electric energy released exter- 

 nally per gram and impulse, in large eels, was found to be 4 micro- 

 calories. This is the maximum external energy which may be obtained, 

 under the condition that the external resistance is approximately equal 

 to the internal. The total electric energy is about 6 times as high as 

 the external, or about 25 micro-calories. These data were obtained 

 on eels of 170 to 180 cm. length. In medium-sized eels of 90 to 120 



