Horse choline esterase

By a careful fractionation of normal horse serum, involving as an essential part of the process a separation of closely related substances by the Schtitz168 foam technique, Bader, Schiitz and Stacey16 obtained a crystalline mucoprotein with high choline esterase activity. This appears to be the first mucoprotein obtained without the use of heat or alcohol, and while it is not yet claimed that the crystalline material is indeed the enzyme itself, arguments are advanced to show that the enzymic activity is closely bound up with mucoprotein structure. 

There is some confusion in the literature regarding the substances designated as anti-choline-esterases (usually shortened to anticholinesterases). The term cholinesterase was first used1 in connexion with an enzyme present in the blood serum of the horse which catalysed the hydrolysis of acetylcholine and of butyrylcholine, but exhibited little activity towards methyl butyrate,... 

Use Biochemical research, determination of phosphorus in insecticides and poisons. (2) Pseudo or nonspecific cholinesterase prepared from horse serum. This esterase hydrolyzes other esters, as well as choline esters. It occurs in blood serum, the pancreas, and the liver. 

By this time, esterases had been described in many animal tissues, and there seemed no reason to suppose that acetylcholine would be exceptionally resistant to their action. In 1932, Stedman et al. (S38) showed that liver esterases from the pig or cat were unable to catalyze the hydrolysis of acetylcholine, and a search was made for the enzyme responsible for the hydrolysis of this choline ester. They went on to describe and purify, for the first time, an enzyme present in horse serum which did catalyze the hydrolysis of acetylcholine. They called this enzyme choline-esterase, and this name—with or without the hyphen— has persisted. 

Similarly, the respective dipeptide choline esters 34 are readily soluble in purely aqueous media (i. e. without added cosolvent) and are converted into the corresponding carboxylic acids under the mildest conditions, and without side attack on the peptide bonds and the N-terminal urethanes, by means of the commercially available butyrylcholine esterase from horse serum. The increased hydrophilicity of peptide choline esters was used advantageously used for the synthesis of peptides and very sensitive peptide conjugates such as lipidated peptides1118-1211, phosphorylated and glycosylated peptides158, 591 and nucleopeptides (Fig. 18-13)176, 781. 

Loewi and Navratil have shown that ACh can be enzymatically inactivated by heart extracts (69). This, however, is not surprising, since, as pointed out by Stedman, Stedman, and Easson (127), esterases are widely distributed in the animal organism and are known to hydrolyze a variety of esters. The important question was whether there is an enzyme which specifically hydrolyzes ACh. Stedman, Stedman, and Easson (l.c.) prepared from horse serum an enzyme which they considered to be an esterase specific for ACh and called it choline esterase. Later investigations do not support the assumption that the enzyme prepared by Stedman, et al. is really a specific choline esterase. There exists, however, an esterase which is specific for ACh. The specificity may be demonstrated by testing the action of an esterase on a number of substrates. In this way, a pattern may be obtained which makes it possible to distinguish the specific choline esterase from other esterases. The esterase in all nerve tissue is either exclusively or predominantly choline esterase. The enzyme is extremely stable. If kept at low temperature and at neutral pH, its activity remains unchanged for many months. The specificity of the enzyme as w eil as other properties will be discussed elsewhere (Nachmansohn and Rothenberg, 131 Nachmansohn, 102). 

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