Effect of succinylphosphatidylcholine on phosphatidylcholine vesicles: structural studies by gel chromatography, electron microscopy and nuclear magnetic resonance.

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.