Vesicle reconstitution from lipid–detergent mixed micelles (original) (raw)
Related papers
Archives of Biochemistry and Biophysics, 1999
The vesicle-to-micelle structural transitions that occurred in the interaction of sodium dodecyl sulfate with phosphatidylcholine vesicles were studied at the equilibrium by means of dynamic light scattering (at different scattering angles) and freeze-fracture electron microscopy techniques. The incorporation of surfactant monomers in the bilayers resulted in an initial contraction of the mixed vesicles formed up to their saturation (size reduction of about 10%). Then, a progressive relaxation of these structures (growth from 170 to 225 nm) and a simultaneous formation of mixed micelles (particles of about 6 nm) occurred. Hence, in this interval "relaxed mixed vesicles" and mixed micelles coexisted in different proportions without formation of intermediate complex aggregates (bimodal size distribution curves). Freeze-fracture electron microscopy showed a direct formation of mixed micelles within the bilayer and their subsequent separation from the vesicle surface without formation of complex intermediate aggregates. This simple process progressed up to the complete vesicle solubilization.
Enzyme-Mediated Formation of Vesicles from DPPC−Dodecyl Maltoside Mixed Micelles
Journal of the American Chemical Society, 1998
An enzymatic procedure for liposome formation through micelle to vesicle transition is described. Amyloglucosidase hydrolysis of dodecyl--D-maltoside (DM) giving dodecyl--D-glucoside (DG) leads to dipalmitoylphosphatidylcholine (DPPC)-based vesicle formation from DPPC-DM mixed micelles. Starting from a 1.8 DM/DPPC molar ratio corresponding to mixed micelles, progressive hydrolysis of DM gives DPPC-DG-DM intermediate aggregates ending with DPPC-DG vesicles upon reaction completion. Initial steps of the process corresponding to the exit of the micellar domain were followed by turbidimetry measurements. Next, the reaction progress was investigated by RP-HPLC, HPLC-GEC, and cryofracture electron microscopy. A constant reaction rate is observed in the micellar domain, while the increase of the lamellae proportion considerably decreases the enzyme catalytic activity. Finally, the enzymatic hydrolysis is significally slowed when closed vesicles are formed. Enzymatic activity is dependent on DM availability in the bulk phase and of the DM/DPPC molar ratio in the aggregates. The presence of mixed micelles or lamellar sheets considerably modulates DM monomer concentration in the aqueous phase. The liposomes formed by the enzymatic process are spherical, unilamellar, and heterogeneous in size with a mean diameter ranging from 10 to 80 nm.
Micron, 1998
The interaction of the amphoteric surfactant dodecylbetaine (C12-Bet) with phosphatidylcholine (PC) liposomes was studied by means of transmission electron microscopy (TEM) and changes in the mean particle size (quasi-elastic light scattering, QELS) and in static light scattering (SLS) of the system were observed during liposome solubilization. A good correlation was found between the TEM diameter of the particles and the mean hydrodynamic diameter (HD) determined by OELS. The aggregates resulting in this interaction were dependent on the C12-Bet concentration in the system. Thus, an initial vesicle growth occurred when the surfactant concentration was 16.66 mol%. Additional surfactant amounts led first to the formation of largest vesicles (HD 306 nm for 37.50 mol% C12-Bet concentration) and second to a fall in the vesicle diameter an in the SLS of the system. Thus, for 47.36 mol% (ReSAT, surfactant to PC molar ratio for liposome saturation), the TEM picture still showed the presence of vesicles albeit with signs of disintegration and vesicle fusion. When additional amounts of surfactant were added to the system the size curve started to show a bimodal distribution. Thus, for 52.38 mol% a sharp curve appeared at 9 nm corresponding to the formation of small particles and the TEM picture showed vesicle disintegration with formation of tubular structures as a crucial intermediate. Up to a surfactant mole percent of 60% progressive vesicle disintegration took place with increasing presence of small aggregates (tubular structures and bilayer fragments) and without formation of complex multilayered structures. The gradual increase in the proportion of these small aggregates (mixed micelles) led to the complete solubilization of liposomes.
Direct formation of mixed micelles in the solubilization of phospholipid liposomes by Triton X-100
Febs Letters, 1998
The vesicle to micelle transition which results in the interaction of the Triton X-100 surfactant with phosphatidylcholine vesicles was studied by means of dynamic light scattering (at different reading angles) and by freeze-fracture electron microscopy techniques. Vesicle solubilization was produced by the direct formation of mixed micelles without the formation of complex intermediate aggregates. Thus, vesicle to micelle transformation was mainly governed by the progressive formation of mixed micelles within the bilayer. A subsequent separation of these micelles from the liposome surface (vesicle perforation by the formation of surfactant-stabilized holes on the vesicle surface) led to a complete solubilization of liposomes.
Mixed micelle-to-vesicle transition in aqueous nonionic phospholipid systems
Journal of Colloid and Interface Science
We have investigated the aggregation behavior in aqueous solutions of mixed systems formed by one nonionic surfactant (Triton X-100 or C12Es) and one phospholipid (egg lecithin or dipalmitoylphosphatidylcholine) by means of quasielastic light scattering and tracer self-diffusion using radioactive labeling. The size of the mixed micellar aggregates depends on the surfactant/lipid ratio and increases with phospholipid content. Dilution of the solutions with the highest phospholipid/nonionic surfactant ratio induces a transition from mixed micelles to vesicles.
Formation of large unilamellar vesicles using alkyl maltoside detergents
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1986
Several alkyl maltosides having different alkyl chain structures and dodecyl maitotrioside were synthesized. The detergent properties of these compounds were investigated with special emphasis on dialysis kinetics during liposome formation. The critical miceile concentration (CMC) and therefore the speed of detergent removal by dialysis mainly depended on the chain length of the hydrophobic part of the molecule, whereas the number of glucose residues in the polar headgroup had no effect on CMC. Liposome preparation was performed through detergent removal by dialysis combined with adsorption to Amberlite XAD-2 as described by Philippot et al. (Philippot, J.R., Mutaftchiev, S. and Liautard, J.P. (1983) Biochim. Biophys. Acta 734, 137-143), leading to a considerable reduction of dialysis volume. Decyl maltoside proved to be a suitable detergent in combination with mixtures of defined synthetic lipids (DOPC/DOPS and DOPC/DOPG). The presence of at least 10% of negatively charged lipid was essential for the formation of unilamellar liposomes.
Journal of Colloid and Interface Science, 1996
vided into three different stages. At low concentration the The solubilization of small unilamellar lecithin vesicles by some surfactant merely distributes between the lipid and water different alkyl sulfate surfactants (C 10 SO 0 4 , C 12 SO 0 4 , and phases and partitions into the vesicle membrane without C 14 SO 0 4 ) was investigated by means of light scattering and cryocausing any major alterations in the bilayer architecture. transmission electron microscopy. All surfactants were found to Then, at a critical, and for each system specific, lipid/surfacinduce vesicle growth at subsolubilizing concentrations and a tant molar ratio the bilayer becomes saturated with surfactant transformation into small globular lipid/surfactant mixed micelles and a breakdown of the vesicular structure is initiated. The at high surfactant concentrations. The surfactant chain length, third and final stage is characterized by the complete solubilihowever, was found to have a profound influence both on the zation of the lipid component into lipid/surfactant mixed amount of surfactant needed for solubilization of the lipid bilayer and on the type of structures formed during the vesicle to micelle micelles. transition. For C 10 SO 0 4 a coexistence between vesicles composed