ENZYMES CONCERNED WITH DIGESTION OF LIPIDS 27 



heart muscle when the latter organ is stimulated by the vagus nerve. 

 Plattner and Bauer 171 offered confirmation for the identity of this sub- 

 stance by proving that the "Vagusstoff" (as acetylcholine was called) and 

 pure acetylcholine were destroyed in an analogous manner by mammalian 

 and by frog bloods. Dale and Dudley, 172 in 1929, were the first to succeed 

 in isolating acetylcholine from animal tissues, i.e., the spleen of horse and 

 ox. Bach 173 demonstrated the production of acetylcholine as the result of 

 stimulation of the vasodilator fibers of the dorsal nerve roots of the rabbit. 



It is now recognized that the presence of acetylcholine is related to the 

 humoral mechanism responsible for the transmission of nerve impulses 

 across synapses, as well as from the nerve endings to the muscles inner- 

 vated by such fibers. According to the classical concept, acetylcholine is 

 set free only at the nerve endings. However, Nachmansohn 174 suggested, 

 in 1945, that acetylcholine is produced everywhere on the neuron surface, 

 and that it is related to electrical changes during activity, and hence to 

 nerve impulse. This concept is further supported by the demonstration 

 that choline acetylase, an enzyme which catalyzes the synthesis of acetyl- 

 choline, is present in the nerve axon, i.e., in that part of the neuron which 

 does not contain nerve endings and cell bodies; hence acetylcholine may 

 also be important for the transmission of the nerve impulse along the 

 axon. 176 Although it is known that the so-called "cholinergic" nerves, 

 which are largely composed of the parasympathetic group, employ acetyl- 

 choline to conduct the nerve impulses across the synapses or to muscle 

 cells, it seems probable that all nerve cells have the capacity to synthesize 

 acetylcholine to a greater or lesser extent. 



Although Dale 176 suggested, in 1914, that an enzyme exists in animal tis- 

 sue capable of destroying acetylcholine, Abderhalden and Paffrath 169 

 first demonstrated the presence of this ester 11 years later. Shortly 

 thereafter, Loewi and Navratil 177 found that the physiological action of 

 acetylcholine is inhibited by extracts of heart tissue; this inactivation of 

 acetylcholine was later proved to result from the action of an enzyme. 178 

 In the course of their studies on the esterases in horse serum and in pig 

 liver, Stedman and collaborators 179 confirmed the fact that acetylcholine is 



171 F. Plattner and R. Bauer, Arch. ges. Physiol. (PHuger's), 220, 180-182 (1928). 



172 H. H. Dale and H. W. Dudley, J. Physiol, 68, 97-131 (1929). 



173 L. M. N. Bach, Am. J. Physiol, 1U, 478-482 (1946). 



174 D. Nachmansohn, Vitamins and Hormones, 3, 337-377 (1945). 



176 D. Nachmansohn, H. M. John, and M. Berman, /. Biol. Chem., 163, 475-480 (1946). 



176 H. H. Dale, J. Pharmacol Exptl. Therap., 6, 147-190 (1914). 



177 O. Loewi and E. Navratil, Arch. ges. Physiol {PHugcr's), 214, 678-688 (1926). 



178 E. Engelhart and O. Loewi, Arch. Exptl Pathol. Pharmakol, 150, 1-13 (1930). 



™ E. Stedman, E. Stedman, and L. H. Easson, Biochem. J., 26, 2056-2066 (1932). 



