COLORIMETRIC PHOSPHOLIPID DETERMINATION WITH ERYTHROSIN-B

Binding of phospholipid vesicles to erythrosin B results in a shift of the absorption maximum of the dye from 528 to 549 nm. This effect was employed to develop a simple, rapid, and sensitive quantification met hod for unilaminar phospholipid vesicles. At room temperature the colo r development of the phospholipid-dye complex at 549 nm is essentially complete in 5 min and only a slight decrease is observed in the follo wing hours. The pH optimum of 4.5 for the assay is related to the tigh t binding at this pH (K-d = 3.6 mu g/ml). A maximal binding of one ery throsin to seven phospholipid molecules is found. The sensitivity of t he assay is high for zwitterionic phospholipids (e.g., 0.023 Delta A(5 49) X ml/mu g for dioleoyl phosphatidyl choline) and lower for anionic phospholipids. The assay depends on the size of the phospholipid lipo somes, indicating the importance of the phospholipid surface area for binding. (C) Academic Press, Inc.