Acetylcholine chloride hydrolysis

All. M. Nakagaki and S. Yokoyama, Base-catalyzed hydrolysis of acetylcholine chloride in the presence of cationic and nonionic surfactants, Bull. Chem. Soc. Jpn. 59,19-23(1986). 

Acetylcholine (ACh) is an ester of choline and acetic acid available in powder form as chloride or bromide salt. It is extremely hygroscopic and rapidly undergoes hydrolysis in a neutral or alkaline medium. 

Hase (H16) studied the effect of pH on the hydrolysis of acetylcholine by horse serum cholinesterase, and his results have been reanalyzed by Laidler (L5) and extensively discussed by Dixon and Webb (D21). The relationship between pH and the rate of hydrolysis of acetylcholine has been used to obtain information on the structure of the active site of the enzyme (B19, W28). Acetylcholine is a particularly suitable substrate for these studies since it does not change its charge in the pH range studied. Similar pH-activity curves have been obtained using other substrates for cholinesterase (H23, S20, P19). Moreover the pH dependence of enzymic activity varies with the buffer system (K3). By investigating the effect of pH and sodium chloride concentration on the rate of hydrolysis of ben-zoylcholine by human plasma cholinesterase, Kalow (K6) deduced that for this substrate, each enzyme molecule contains at least two binding sites which differ in their dependence on pH. Michaelis constants and maximum hydrolysis velocities were measured for each of the two binding sites, and pK values of the enzyme-substrate complexes were found to be 5.2, 6.7, and 9.2 for one site, and 5.2, 7.0, 8.4, and 8.8 for the other. 

The effects of inorganic salts on plasma cholinesterase (E16) are largely contradictory. Fruentova (F9) reported that divalent cations are more effective inhibitors of horse serum cholinesterase than are monovalent ions, whereas divalent ions are frequently reported to have a marked activating effect (H38, T8, VI). Lithium and sodium nitrates have been shown by in vitro studies of the reaction of human plasma cholinesterase with benzoylcholine to have identical inhibition profiles (W21), while sodium and potassium chlorides had very similar inhibitory actions on the hydrolysis of acetylcholine by human plasma (H47). Silver nitrate, copper sulfate, and mercuric chloride are powerful inhibitors of F. polycolor butyrylcholinesterase (N2). Cohen and Oosterbaum (C12) concluded that activation by cations occurring at the usual substrate concentration is highly dependent on the experimental conditions. This supposition is very relevant to the somewhat random choice of buffers and substrates in the work reported above. 

The most generally used method (Warburg manometric method) depends on the evolution of carbon dioxide from bicarbonate solutions when acetic acid is produced by hydrolysis of acetylcholine (3). The conversion of acetylcholine and certain other esters into the corresponding hy-droxamic acids when treated with hydroxylamine has been described by Hestrin (42) and a photometric method, depending on the ferric chloride reaction with acetic acid, has been reported by Abdon and Uvnas (1). A later report by Mitchell and Clark (61) involves the colorimetric measure-... 

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