26 II. DIGESTION AND ABSORPTION OF FATS 



buted in nature. In the animal, the highest concentration was found in the 

 kidney, with a decreasing activity in the following order: small intestine, 

 spleen, liver, testes, pancreas, large intestine, brain, ovary, bone, suprare- 

 nals, lung, blood vessels, cardiac muscle, and skeletal muscle. 159 The 

 optimum pR was found to be 7.5, and the optimum temperature 159 about 

 37 °C. It was reported that artificial hydrolecithins were broken down as 

 readily as was the parent lecithin. 160 For a more complete discussion of 

 lecithinases A, B, C, and D, the reader is referred to Volume I of this work. 

 c. Cholinesterases. (a) Introduction. Cholinesterases are enzymes, 

 present exclusively in animal tissues, which are capable of catalyzing the 

 breakdown of acetylcholine into acetic acid and choline: 



O O 



+ HOH + 



CH 3 COCH 2 CH 2 N(CH 3 ) 3 > CH 8 COH + HOCH 2 CH 2 N(CH 3 ) 3 



Acetylcholine Acetic Choline 



acid 



The Hydrolysis of Acetylcholine with Cholinesterase 



The subject of cholinesterase has been reviewed by Ammon, 161 Brown, 162 

 Werle, 163 Zeller 164 and most recently by Nachmansohn and Wilson 165 and 

 for a second time by Ammon. 166 The role of cholinesterase and of acetyl- 

 choline in the transmission of nerve impulses across the neuromuscular 

 junction was discussed at a conference (1951-1952) of the Muscular Dys- 

 trophy Association of America. 167 



(6) Discovery of Acetylcholine and Cholinesterases. Although acetyl- 

 choline was discovered as early as 1867 by Baeyer, 168 it was not known until 

 58 years later that this substance has a widespread distribution in animal 

 tissues, and that it plays a most dramatic role in the functioning of nervous 

 tissue. The discovery of cholinesterase followed the demonstration of 

 acetylcholine. Abderhalden and Paffrath 169 announced the presence of 

 this ester in the intestine of the horse and pig. 



Loewi 170 in 1921, first reported that an active compound is set free from 



161 R. Ammon, Ergeb. Enzymforsch., 4, 102-110 (1935). 



162 G. L. Brown, Physiol. Revs., 17, 485-513 (1937). 



163 E. Werle, Fermentforschung, 17, 230-257 (1943). 



164 E. A. Zeller, Advances in Enzymology, Vol. VIII, Interscience, New York and 

 London, 1948, pp. 459-495. 



165 D. Nachmansohn and I. B. Wilson, in Advances in Enzymology, Vol. XII, Inter- 

 science, New York and London, 1951, pp. 259-339. 



166 R. Ammon, Ergeb. Enzymforsch., 9, 35-69 (1943); Chem. Zentr., 1943, II, 1719. 



167 D. Nachmansohn, Proc. 1st & 2nd Med. Conf. Muscular Dystrophy Association, of 

 America, New York, Apr. 14-15 1951, May 17-18, 1952, pp. 2-15. 



168 A. Baever, Ann., 142, 322- 326 (1867). 



189 E. Abderhalden and H. Pf ffrath, Fermentforschung, 8, 299-307 (1925). 

 »° O. Loewi, Arch. ges. Physi rt. (Pftuger's), 189, 239-242 (1921). 



