NACHMANSOHN: CHEMICAL MECHANISM IN NERVES 409 



breakdown, but it does not interfere with the transfer of energy-rich 

 phosphate bonds, as has been shown by Ochoa.^^ 



The enzyme has also been extracted from powder of acetone dried 

 brain.2^'^° Extracts prepared from one gram of powder form 1.0-2.0 

 mgs. of ACh per hour. Since acetone inactivates chohnesterase, this 

 enzyme is largely, or sometimes completely, inactivated in the extracts 

 prepared from powder of acetone dried brain, so that addition of eserine 

 may have either a small effect or practically none on the formation of 

 ACh. Adenosine triphosphate is also removed in extracts from acetone 

 dried brain. No addition of fluoride is, therefore, required. For in- 

 stance: In one experiment, 820 ^g. of ACh were formed per gram and 

 hour, with no eserine 780 ^g., and without fluoride 810 ftg. It has, 

 thus, been demonstrated that the enzyme mechanism responsible for 

 the formation of the ester is not identical with the hydrolyzing enzyme. 



The enzyme requires the presence of potassium in high concentration, 

 close to that found in brain. It contains active sulfhydryl groups 

 which are readily inactivated by monoiodoacetic acid or copper in low 

 concentration. The — SH groups are easily oxidized by air. On di- 

 alysis, the enzyme rapidly loses its activity. Addition of potassium ion 

 and 1 ( + ) glutamic acid or cysteine reactivates partly. 1 ( + ) alanine, 

 also, has some effect; other amino acids have either a weak effect or 

 none. Citric acid has an effect nearly as strong as glutamic acid, 

 whereas dicarboxylic acids have practically no effect.^^- ^° 



The longer the dialysis is carried on, the weaker is the reactivation 

 by the compounds mentioned. The experiments suggest that choline 

 acetylase requires, a coenzyme for its activity. The coenzyme has 

 now been found. In contrast to the enzyme which occurs only in 

 nerve tissue, the coenzyme has been extracted from brain, liver, heart, 

 and skeletal muscle (Nachmansohn and Berman^^). The coenzyme 

 has been purified to a certain degree by treatment with barium salt, 

 which precipitates the coenzyme. The purification, however, is still in 

 progress. The coenzyme not only reactivates the dialyzed enzyme, 

 but increases considerably the undialyzed enzyme preparations. 

 Marked activation has been obtained in this way, especially in extracts 

 from lobster nerve, rabbit's optic nerve, ajid electric tissue. Of special 

 interest is the evidence for the presence of choline acetylase in the 

 optic nerve. The possibility of a role of ACh in sensory nerves has 

 been a matter of controversy for many years, since the ester was not 

 found in such nerves, whereas chohnesterase is present in concentra- 

 tions in an order of magnitude similar to that in motor nerves. The 

 presence of choline acetylase in the optic nerve is further support for 



