STRUCTURE-FUNCTIONAL EFFECTS OF A SERIES OF ALCOHOLS ON ACETYLCHOLINESTERASE-ASSOCIATED MEMBRANE-VESICLES - ELUCIDATION OF FACTORS CONTRIBUTING TO THE ALCOHOL ACTION

Structure-functional effects of a series of alcohols on acetylcholines terase (AChE) derived from Torpedo californica were investigated. No s ignificant effect on the soluble form of the enzyme was observed, but a marked biphasic effect on the activity of the membrane-associated fo rm of the enzyme was found: it increased to maxima of 115 +/- 2% at 40 mM ethanol, 123 +/- 2% at 10 mM propanol, and 114 +/- 2% at 10 mM t-b utanol; declined with further increases in alcohol concentration; and then leveled off. Significantly, no increase was observed with n-butan ol. The effect on membrane-associated AChE activity was in the order o f propanol > t-butanol > ethanol > n-butanol, suggesting that the site of action of alcohol was small and could not accommodate straight-cha in alcohols longer than propanol. Comparison of the results for solubl e AChE and membrane-associated AChE activity indicated the involvement of the membrane in alcohol action. Fluorescence steady-state polariza tion (P) measurements of Torpedo membrane vesicles showed that membran e fluidity increased with increasing [alcohol], as indicated by a decr ease in polarization (Delta P = -0.010 +/- 0.003, -0.062 +/- 0.003, -0 .017 +/- 0.002, and -0.011 +/- 0.002 in the presence of 60 mM ethanol, propanol, n-butanol, and t-butanol, respectively). Alcohol-induced in crease in membrane fluidity was in the order propanol > n-butanol > t- butanol, ethanol, suggesting that both lipid solubility and molecular size of alcohols could be important if alcohols must fit into membrane lipid domains in order to affect membrane fluidity. The biphasic effe ct of alcohol action on membrane-associated AChE activity is discussed in terms of membrane fluidity, lipid solubility, molecular size of al cohol, enzyme-lipid interaction, site of alcohol action, and a direct interaction of alcohol with the enzyme. (C) 1995 Academic Press,Inc.