Structural changes in membranes produced by the binding of small amphipathic molecules

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Abstract
In their interactions with membranes, amphipathic small molecules exhibit detergent-like properties. At sufficiently high concentrations (above their critical micelle concentrations, if they form micelles), they substantially dissolve membranes. At lower concentrations, between maximally antihemolytic and lytic, the amphipaths are shown here to significantly perturb membrane structure. Each of 6 small-molecule amphipaths [chlorpromazine, methochlorpromazine, tetracaine, indomethacin, decanol, 2,4-dinitrophenol] was shown by hygroscopic desorption filtration to induce the extraction of small but significant amounts of membrane components, particle in the form of vesicular fragments, from human red blood cell membranes. These extracts were enriched in the lipid to protein ratio as compared to the intact membrane, and the protein composition highly unrepresentative. A similar set of extractions from rabbit sarcoplasmic reticulum membranes was induced by the 6 amphipaths. Small-molecule amphipaths at concentrations lower than lytic apparently promote gross redistributions of components in the plane of a membrane that result in the observed extractions.