Abstract
The influence of inorganic salts on the kinetics of the reactions of acetylcholinesterase with neutral and cationic substrates at 25°C and pH 7.5 in the range of salt concentrations from physiological ionic strength up to nearly saturated solutions has been studied. In both types of substrates, the electrolytes had no influence on the acetylcholinesterase active site acylation and deacylation rate constants—the influence of the salts appeared only in the dissociation constants of the enzyme-substrate (ES) complexes. Two mechanisms were found to account for the observed effects: the primary (electrostatic) salt effect, and the salt influence on the solubility of substrates. In addition, an inhibitory effect of some 2 : 1 and 1 : 2 electrolytes (Na 2SO 4, MgCl 2, CaCl 2, SrCl 2, BaCl 2) appeared at high concentrations. The results suggest that substrates in acetylcholinesterase-catalyzed reactions are extracted into the enzyme microphase at the stage of ES-complex formation and further substrate transformation proceeds inside the enzyme.
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