PROPERTIES OF LIPID BILAYER MEMBRANES SEPARATING 2 AQUEOUS PHASES - COMPOSITION STUDIES

The composition of thin synthetic lipid membranes formed from solutions of (a) phosphatidylethanolamine in decane and (b) phosphatidylethanolamine and cholesterol in decane have been determined. The thin black membranes were formed with radioactively labeled components of high specific activity, stabilized by means of fixation with La(NO3)3 and KMmO4 (Henn, Decker, Greenawalt & Thompson, 1967) and sampled. The results indicate that the molar ratio of decane: phospholipid in cholesterol free membranes is 11.8 ± 3.4, and 10.5 ± 1.8 in membranes containing cholesterol. The cholesterol: phospholipid ratio is 1.5 ± 0.2 in these synthetic films. A consideration of the calculated and measured surface area per phospholipid molecule and the electron micrographs of fixed membranes leads to the conclusion that these films are bilayers of phospholipid containing an appreciable amount of decane which have in addition occasional thicker regions or lenses of trapped decane. This structure is able to account for the measured physical properties of the bilayer membrane. © 1968.