New vesicle formation upon oleate addition to preformed vesicles

The size distribution of new vesicles formed after addition of oleate in different forms to preformed egg yolk phosphatidylcholine (EggPC) vesicles was studied by gel exclusion chromatography. The addition of oleate to preformed vesicles resulted in the formation of new small vesicles. Fission of preformed vesicles incorporated by oleate and partial solubilization of the vesicles by addition of oleate in micellar form were involved in the process of the new small vesicle formation.     

Size control of mixed egg yolk phosphatidylcholine (EggPC)/oleate vesicles

The size distribution after addition of oleate surfactant to preformed Egg yolk phosphatidylcholine (EggPC) vesicles was investigated by gel filtration chromatography combining with dynamic light scattering. Phospholipid and oleate concentration, fluorescence intensity and size of the vesicles were measured for each elution fraction. The spontaneous vesiculation of oleate at pH 8.5 was accelerated in the presence of preformed EggPC vesicles. The size distribution of newly formed vesicles was dependent on the preformed vesicular size. For example, oleate addition to large preformed vesicles (230 nm) resulted in altering of vesicles to both larger and smaller than preformed ones, while addition of oleate to small preformed vesicles (50 nm) led to the formation of only larger vesicles without exhibition of newly small vesicles. The combinations of gel filtration chromatography and dynamic light scattering could provide more detailed insight into the size change of newly formed vesicles.     

Effect of preformed egg phosphatidylcholine vesicles on spontaneous vesiculation of oleate micelles

An addition of oleate micellar solution to two original sizes (180 nm and 50 nm) of preformed vesicles was studied using gel exclusion chromatography, dynamic light scattering and freeze fracture electron microscopy. The effect of molar ratios of phospholipid and oleate on size distribution of newly formed vesicles was investigated by varying molar concentrations of these two components. After adding an equiamount of oleate to 180 nm-preformed vesicles or 50 nm-preformed vesicles, a relatively monodisperse population of newly formed vesicles was detected. For the high amount of oleate addition to two original sizes of preformed vesicles, the results were quite different. New large vesicles and a number of new small vesicles were observed in samples of mixed EggPC/oleate suspension in the presence of preformed vesicles with 180 nm of size, whereas, only some new large vesicles were detected in samples of mixed EggPC/oleate suspension in the presence of preformed vesicles with 50 nm of size. We assumed that the number of new small vesicles, with size close to preformed vesicles, increased in the latter case. The transformation of mixed EggPC/oleate micelles to mixed vesicles was investigated. The results showed that transformation of mixed EggPC/oleate micelles to vesicles was remarkably faster than transformation of mere oleate micelles to vesicles. The above findings suggested that new mixed EggPC/oleate vesicles with small size were presumably formed by partial solubilization.