Membrane partitioning isotherms of GM2AP from sedimentation experiments. All experiments were performed in 50 mM NaOAc buffer, pH 4.8, with final GM2AP concentration of 10 μM. Figures plot the fraction of GM2AP bound to the lipid vesicles. Protein was incubated with 0 to 500 μM large unilamellar vesicles for 20 min and followed by ultracentrifugation at 100,000 × g for 1 h. The protein concentration in the supernatant was measured by fluorescamine labeling. The top panel shows results for POPC vesicles. The bottom panel shows results for POPC:POPG (7:3), circles; POPC:GM2 (9:1), squares; POPC:BMP:GM2 (7:2:1), down triangles. Lines are fits to the data as described within the text. Error bars represent standard deviations of three separate measurements.