Fig. 1. Detergent analyses. (A) Diagrammatic representation of detergent–membrane interaction. Loosely packed raft-depleted plasma membrane (RDPM) accommodates more detergent prior to saturation (higher saturation point; plate 1) than tightly packed raft (plate 2). After saturation occurs, mixed micelles form, dissolving the membrane. Lipids in RDPM are more readily incorporated into micelles (steeper solubilization slope; plate 3) than are raft lipids (plate 4). (B) Detergent assay. Membrane dissolution is followed as changes in optical density (OD) over time. End points are recorded as optical density just prior to detergent addition (arrow). Inset: normalized end points as a function of detergent/lipid (D/L) ratios with sigmoidal regression. (C) Analysis. Sigmoidal regression with D/L values of 2nd-derivative peaks marked (points a and b) with the linear regression between points a and b superimposed. Inset: 2nd derivative with peaks marked (points a and b). Saturation point (i.e. where solubilization becomes dominant over detergent incorporation) is defined by point a. Solubilization slope is defined as the slope of the linear regression between points a and b.

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