The distribution of cholesterol in bilayers of phosphatidylcholines as visualized by freeze fracturing

Abstract The crystallization behavior of bilayers of synthetic phosphatidylcholines in the presence of cholesterol was investigated by freeze fracturing. 1. 1. Below the lipid-phase transition, cholesterol is randomly distributed over the lateral plane of a bilayer of the single species dimyristoylphosphatidylcholine, as far as can be detected within the lateral resolution of freeze fracturing. 2. 2. In an equimolar mixture of dilauroyl- and dimyristoylphosphatidylcholine, which shows cocrystallization, cholesterol is distributed randomly in the bilayers below the phase-transition temperature. 3. 3. In an equimolar mixture of dipalmitoyl and 1-palmitoyl-2-oleoylphosphatidylcholine, which shows monotectic behaviour, cholesterol interacts preferentially with the liquid crystalline species 1-palmitoyl-2-oleoylphosphatidylcholine when the other component dipalmitoylphosphatidylcholine passes from the liquid crystalline to the gel state upon cooling the mixture.