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 acetylcholinesterase (AChE) derived from Torpedo californica were investigated. No significant effect on the soluble form of the enzyme was observed, but a marked biphasic effect on the activity of the membrane-associated form 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-butanol; declined with further increases in alcohol concentration; and then leveled off. Significantly, no increase was observed with n-butanol. The effect on membrane-associated AChE activity was in the order of propanol > t-butanol > ethanol > n-butanol, suggesting that the site of action of alcohol was small and could not accommodate straight-chain alcohols longer than propanol. Comparison of the results for soluble AChE and membrane-associated AChE activity indicated the involvement of the membrane in alcohol action. Fluorescence steady-state polarization (P) measurements of Torpedo membrane vesicles showed that membrane fluidity increased with increasing [alcohol], as indicated by a decrease in polarization (delta P = -0.010 +/- 0.003, -0.062 +/- 0.0003, -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 increase 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 effect of alcohol action on membrane-associated AChE activity is discussed in terms of membrane fluidity, lipid solubility, molecular size of alcohol, enzyme-lipid interaction, site of alcohol action, and a direct interaction of alcohol with the enzyme.