Physical Properties of Phosphatidylcholine Vesicles Containing Small Amount of Sodium Cholate and Consideration on the Initial Stage of Vesicle Solubilization.

Abstract

Sodium cholate (Na-chol) is a physiological detergent. Its solubilizing properties are important in several fundamental biophysical and biochemical processes. This includes disintegration of biomembranes to mixed micelles, 1) reconstitution of membrane proteins and lipids to functional supramolecular structures (vesicles in most cases) 2,3) and preparation of homogeneous lipid vesicles of controlled sizes. 4,5) The vesicle destruction mechanism has been studied in connection with the reconstitution of membrane proteins after purification in detergent solutions. Concerning the disintegration from mixed vesicles to mixed micelles by Nachol, many studies have concentrated on the variation in morphology and properties of mixed aggregates.6,7) Consequently, the solubilization process of phosphatidylcholine (PC) vesicles is summarized as follows; addition of very small amounts of Na-chol to vesicles results in the partitioning of Na-chol between the water and lipid phases. At a further increased detergent concentration, vesicles containing a large amount of Na-chol are formed, whose behavior, such as fusion of small vesicles to larger ones, is found to be different from that of PC vesicles containing large amounts of nonionic detergents (i.e. octylglucoside).5) At a still further increased detergent concentration, the Na-chol-containing vesicles disintegrate into intermediate structures, and finally into mixed micelles. 8,9) As far as intermediate structures are concerned, structural changes from vesicles to perforated vesicles, to discoidal sheets, 10) or to rod-like structures 11) have been reported. As described above, the incorporation of Na-chol into vesicular membranes remarkably influences the structures and properties of PC vesicles. However, little is known about the effects of the incorporation of Na-chol on the behavior of membranes at a molecular level, although it is important for further detailed studies on the mechanism of vesicle disintegration. The present report deals with the influence of addition of small amounts (insufficient to destroy vesicles) of Na-chol on several physicochemical properties of PC small unilamellar vesicles (SUV). Similar to the previous reports, 12-14) ESR spectra of a spin label 12-doxylstearic acid (12-DS) are applied to monitor the variation in properties and structures of the mixed PC SUV. Differential scanning calorimetry (DSC) and z potentials measured with electrophoretic light scattering methods were also employed for observing the variation in the properties of PC SUV induced by Na-chol. The obtained results will be considered in connection with the initial stage of the solubilization of PC vesicular membranes. ExperimentalMaterials Phosphatidylcholine isolated from egg yolk (EPC) (purity approximately 98.8%) was purchased from Nihon Yushi (Tokyo, Japan). Sodium cholate and cholesterol of guaranteed degree were obtained from Nacalai Tesque (Kyoto, Japan). Synthetic dimyristoylphosphatidylcholine (DMPC) (purity ca. 99%) as well as 5-, 12-, and 16-DS were purchased from...

Cholesterol Determines and Limits rHDL Formation from Human Plasma Apolipoprotein A-II and Phospholipid Membranes

“…The sharp transition corresponds to a relatively pure PC phase, whereas the other, which like FC/DMPC MLV exhibits a broad endotherm, is a cholate/DMPC phase. 29 Thus, on the basis of our data, in the presence of cholate the apolipoproteins preferentially associate with the relatively pure DMPC phase that gives rise to the sharp transition and from which most FC is excluded.…”

Aggregation Phenomena on the Ternary Ionic−Nonionic Surfactant System: Didodecyldimethylammonium Bromide/Octyl-β-d-glucopyranoside/Water. Mixed Microaggregates, Vesicles, and Micelles

“…In this range, the single-chain surfactant is incorporated into the vesicle membrane depending on the partition equilibrium between the vesicle bilayer and the aqueous phase, without the occurrence of the breakdown of vesicles. This feature affects vesicle properties, such as permeability, fluidity, etc., and offers a variety of practical applications. ,,,− ,,− For all the above- mentioned reasons, some investigations concerning vesicle/surfactant studies have been focused on the subsolubilizing (sublytic) concentration region. ,, However, almost nothing has been reported in the extremely diluted concentration range, where a different kind of colloidal aggregate, intermediate between the monomeric and the vesicle stages, may appear.…”

“…This feature affects vesicle properties, such as permeability, fluidity, etc., and offers a variety of practical applications. 1,7,8,[12][13][14]25,[27][28][29][30][31][32] mentioned reasons, some investigations concerning vesicle/ surfactant studies have been focused on the subsolubilizing (sublytic) concentration region. 5,14,33 However, almost nothing has been reported in the extremely diluted concentration range, where a different kind of colloidal aggregate, intermediate between the monomeric and the vesicle stages, may appear.…”

Process of Destruction of Large Unilamellar Vesicles by a Zwitterionic Detergent, CHAPS: Partition Behavior between Membrane and Water Phases

“…This result is consistent with the results of our previous study showing that the rotational correlation time of 12-DS increased after the addition of sodium cholate to EggPC liposomes. 36) In summary, we propose the destruction mechanism of LUVs by CHAPS as follows: stage 1 is the distribution of CHAPS through vesicle membranes. No significant structural change is observed.…”