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THE LACK OF SPECIFICITY TOWARDS SALTS IN THE ACTIVATION OF CHOLINE ACETYLTRANSFERASE FROM HUMAN PLACENTA
Author(s) -
Hersh Louis B.
Publication year - 1979
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1979.tb04585.x
Subject(s) - divalent , chemistry , choline , substrate (aquarium) , medicinal chemistry , inorganic chemistry , choline acetyltransferase , enzyme , acetylcholine , stereochemistry , biochemistry , organic chemistry , medicine , oceanography , endocrinology , geology
— The effects of monovalent and divalent anions on the choline acetyltransferase reaction have been determined at high (5.0 mM) and low (0.58 mM) choline. At 0.58 mM‐choline, both monovalent and divalent anions activate the enzyme ±9 fold; however, at 5.0mM‐choline, monovalent anions activate the enzyme ±25 fold, while divalent anions activate ±9 fold. Both monovalent and divalent anions show uncompetitive activation with respect to choline. When either dimethylaminoethanol, N ‐(2‐hydroxyethyl)‐ N ‐methyl piperidinium iodide, or N ‐(2‐hydroxyethyl)‐ N ‐propyl pyrrolidinium iodide was substituted for choline, activation by monovalent or divalent anions was only 2.5‐4 fold. With AcCoA as substrate the ChA reaction can be increased ±20 fold by increased salts; however, with acetyl dephosphoCoA as substrate, the reaction is insensitive to the salt concentration. Similar salt effects on the ChA reaction, as measured in the direction of acetylcholine synthesis, have been demonstrated in the reverse reaction. In addition, inhibition of the forward reaction by acetylcholine has been measured as a function of sodium chloride concentration. Although the K 1 for acetylcholine increases with increasing salt, this change in K 1 , parallels the increase in the K m for choline. These results support the hypothesis that both monovalent and divalent anions activate choline acetyltransferase by the same singular mechanism; which is to increase the rate of dissociation of coenzyme A from the enzyme.