Figure 1.

Specific binding of SA-Ro complex to PE. (A) Ro conjugated with ¹²⁵I-SA-Ro bound selectively to PE-containing liposomes. ¹²⁵I-SA-Ro was incubated with various concentrations of liposomes composed of egg yolk phosphatidylcholine (PC), dicetyl phosphate and cholesterol (respective molar ratios, 0.75/0.1/1.0) without (•) or with PE (○), phosphatidylserine (PS, □), phosphatidylinositol (PI, ▪), phosphatidic acid (PA, ▴), or cardiolipin (CL, ▵) each at a molar ratio to egg yolk phosphatidylcholine of 0.25. (B and C) Ro conjugated with FL-SA stained permeabilized erythrocyte membranes, but not intact erythrocytes. FL-SA-Ro was added to intact (B) or SLO-treated erythrocytes (C) at 4°C. The intact erythrocytes were permeabilized with SLO after FL-SA-Ro treatment and both the samples were washed and photographed. FL-SA-Ro fluorescence and phase contrast of same specimens, respectively, are shown. Intact erythrocytes were virtually unstained, whereas permeabilized membranes were labeled uniformly. (D) Binding of ¹²⁵I-SA-Ro to intact and permeabilized erythrocytes. Permeabilized erythrocytes bound 10 times more ¹²⁵I-SA-Ro than intact erythrocytes and preadsorption of ¹²⁵I-SA-Ro with PE-containing liposomes abolished this binding (n = 3). (Bar = 10 μm.)