The shape of the gel to liquid crystalline phase transition of dielaidoylphosphatidylethanolamine is markedly dependent on the method of sample preparation

Phosphatidylethanolamines are known to exhibit asymmetric phase transitions with a low temperature shoulder. However, in this work we demonstrate that suspensions of dielaidoylphosphatidylethanolamine can be prepared which exhibit very sharp and only slightly asymmetric phase transitions. Such preparations are made either by isolating a rapidly sedimenting fraction of a vortexed suspension of this lipid or by dialyzing a suspension which had been hydrated at pH 9.2 to pH 7.2. Smaller aggregates of the lipid can be isolated from the supernate of a vortexed suspension of dielaidoylphosphatidylethanolamine after removal of the rapidly sedimenting fraction or it can be produced by sonication of a sample at pH 9.2 followed by dialysis to pH 7.2 Such preparations exhibit very broad transitions and the transition temperature is shifted to lower values. These results demonstrate that the shape of the phase transition of dielaidoylphosphatidylethanolamine is particularly sensitive to the method of sample preparation. Furthermore, an asymmetric phase transition with a low temperature shoulder is not necessarily an intrinsic property of phosphatidylethanolamines.