protein content of the membrane preparations was determined using the bicinchoninic acid bca assay using bovine serum albumin as standard small 100 nm unilamellar vesicles suv containing dmpc dmpg dmps and dmpe and cholesterol were prepared in 0 02 m phosphate buffer ph 6 8 by sonication and extraction briefly 1 5 mg of total lipid was dissolved in 1 5 ml of chcl 3 meoh 3 1 v v aliquots 408 u03bcl were removed and evaporated under a stream of nitrogen and the lipids further dried in vacuo overnight the lipids were then resuspended in 600 u03bcl of 0 02 m sodium phosphate buffer ph 6 8 the resulting lipid dispersion was sonicated in a bath type sonicator until clear and then extruded 17 times through 100 nm pore diameter polycarbonate filters using liposofast apparatus avestin ottawa canada to obtain 100 nm swv the mixed lipid vesicles contained 80 w w 60 w w 40 w w 30 w w or 0 w w cholesterol the remaining lipid comprised a mixture of dmpc dmpe dmps dmpg in a ratio of 75 20 2 5 2 5 by weight binding experiments were carried out with a biacore x analytical system biacore uppsala sweden using an l1 sensor chip biacore as supplied by the manufacturer it will be appreciated that other types of biosensor may also be used preferably provided that the chip surface is such that the bound lipid material is able to retain a.