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

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, we show here that the amphipaths significantly perturb membrane structure. Each of six small-molecule amphipaths was shown by hygroscopic desorption filtration to induce the extraction of small but significant amounts of membrane components, partly in the form of vesicular fragments, from red blood cell membranes. These extracts were enriched in the lipid to protein ratio as compared to the intact membrane, and the protein composition was highly unrepresentative. A similar set of extractions from sarcoplasmic reticulum membranes was induced by the six amphipaths. We conclude that small-molecule amphipaths, at concentrations lower than lytic, promote gross redistributions of components in the plane of a membrane that result in the observed extractions.