416 IMMUNO-CATALYSIS 



therefore be worthwhile to discuss certain properties of acetylcholine 

 before consideration of its role in anaphylaxis. 



a. Destruction and Synthesis of Acetylcholine. Cholinesterase. 



Acetylcholine esterase is the enzyme which destroys acetylcholine 

 (Loewi and Navratil, 1926). According to Nachmansohn, et al. 

 (1948), a highly purified enzyme preparation containing 1 mg. of 

 protein was capable of hydrolyzing 60 g. of acetylcholine in one hour. 



The enzyme is found in nerve and muscle. They are the only 

 tissues in which this specific enzyme has been found, whereas all 

 other tissues contain distinctly different types of esterase (Nachman- 

 sohn, et al., 1947). Other tissues and serum contain enzymes capable 

 of hydrolyzing acetylcholine, often in high concentration, but appar- 

 ently of slightly different specificity than the muscle or nerve 

 esterase. 



Choline Acetylase. This enzyme mediates the synthesis of acetyl- 

 choline from choline and acetate. The essential role of acetylcholine 

 in the conduction of the impulse in the muscle fiber as that in the 

 nerve fiber necessitates that its synthesis through an enzyme in these 

 tissues be insured. The synthesis of acetylcholine by isolated brain 

 (Quastel, et at, 1936), and in nerve endings (Macintosh, 1941) has 

 been reported. Nachmansohn, etal. (1947) demonstrated the presence 

 of choline acetylase in extracts from pigeon breast muscle, skeletal 

 muscle of guinea pig, and cardiac muscle of rabbit and guinea pig. 

 The test-systems contained choline, acetate, eserine, potassium, mag- 

 nesium, cysteine, adenosine triphosphate and coenzyme (probably a 

 pantothenic acid derivative, Lipmann, et al. 1947). Choline acetylase 

 was reported to be completely absent in liver and kidney extracts 

 similarly prepared and tested. In these reactions eserine serves as the 

 inhibitor of choline esterase to permit the preservation of synthesized 

 acetylcholine. Cysteine serves to maintain the -SH groups of the 

 enzyme choline acetylase. Potassium is necessary for the activity of the 

 enzyme. Coenzyme which probably contains a pantothenic acid deriva- 

 tive is necessary for the acetylation of choline. Acetate is converted 

 to acetylphosphate by receiving an energy rich phosphate from adeno- 

 sine triphosphate. Acetylphosphate donates its acetyl group to choline. 



b. "Muscarinic" and "Nicotinic" Actions of Acetylcholine, Ace- 

 tylcholine has two types of action in the body. Resembling closely the 

 action of the alkaloid muscarine, acetylcholine acts at or beyond the 



