Complement-Dependent Changes in the Emission Anisotropy of a Fluorescent Probe in Liposomes

When liposomes carrying Forssman hapten are treated with anti-Forssman IgM and guinea pig serum as a source of complement, trapped ⁸⁶Rb⁺ is released. The emission anisotropy (r) of added 1,6-diphenyl-1,3,5-hexatriene (DPH) has been measured in liposomes that were treated with antibody and complement and then separated from released ⁸⁶Rb⁺ and most serum protein by agarose 50M gel exclusion chromatography. In untreated control dimyristoyl lecithin/cholesterol liposomes the anisotropy of DPH is r=0.315 (25°C). In controls treated with guinea pig serum but not with antibody, the r value decreases. For example, on addition of 150 µl serum to 0.17 µmole of liposomal phospholipid, the r value was 0.251. When antibody was included the r value declined to 0.179. Thus, a difference of 0.072 is attributable to complement. In a similar experiment, 69 µl C7-deficient human serum added to 0.084 µmole liposomal phospholipid in the presence of antibody gave r=0.287.