Effect of succinylphosphatidylcholine on phosphatidylcholine vesicles: structural studies by gel chromatography,...

The effect of an aqueous dispersion of succinylphosphatidylcholine on an aqueous suspension of phosphatidylcholine vesicles was studied by gel chromatography, freeze-fracture electron microscopy and proton nuclear magnetic resonance with Mn2+ (broadening paramagnetic reagent). Total phospholipid concentrations were in the range 10--20 mM. Succinylphosphatidylcholine is in micellar form and behaves as a detergent. The structures obtained depend on the molar percentage of succinylphosphatidylcholine. Above a succinylphosphatidylcholine molar percentage of 60%, mixed micelles are formed, assumed to be essentially spherical. Below a succinylphosphatidylcholine molar percentage of 30%, principally mixed vesicles are observed, with an external diameter of 215--240 A, and an almost constant internal volume. Between 30 and 60% of succinlyphosphatidylcholine, a mixture of these structures is obtained; rod-shaped profiles are also observed in electron microscopy, which may correspond to sections of leaky vesicles or to a new kind of cylindrical micelle.