[Mechanism of micelle-vesicle transformation and control of vesicular sizes and properties].
The mechanism of vesicle-to-micelle or micelle-to-vesicle transition was studied in order to control sizes and fluidities of vesicles during periods of preparation. Dependence of particle sizes measured by quasi-elastic light scattering, turbidities, fluidity parameters monitored by ESR spectroscopy, and morphological changes of mixed aggregates of egg yolk phosphatidylcholine (EPC) and a detergent (octylglucoside (OG) or sodium cholate (Na-chol)) on detergent concentration provided a model of vesicle destruction. It possessed three phase transition points, and proceeded in a stepwise fashion: vesicles, small particles containing large amounts of detergents (SUV(*)), intermediate structures, and mixed micelles. Vesicle formation on removal of detergents from micelles proceeded oppositely. Micelle-vesicle transition mechanism was common to all detergents examined. The feature of the mechanism was the presence of SUV(*). Next, SUV(*) was prepared by adding appropriate amount of a detergent to small unilamellar vesicles obtained by sonication. Time-dependent size growth of the SUV(*) was remarkable in the case of OG-containing SUV(*), but was insignificant in the case of Na-chol-containing SUV(*), suggesting the size determining step to be the stage of the SUV(*). The tendency to produce large or small vesicles from micelles was related to the absence or presence, respectively, of a net charge in the detergent molecule. The fluidities of EPC micelles containing small amounts of a detergent possessing a steroidal structure (e.g., Na-chol or CHAPS) were significantly smaller than the corresponding values of a detergent without a steroidal structure (e.g., OG), suggesting a method of control of orderliness of hydrocarbon chains in EPC vesicles.
Kashiwagi
Hiroshi
H
Division of Pharmaceutical Sciences, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Sugitani, Toyama City, Japan. kasiwagi@pha.u-toyama.ac.jp
Ueno
Masaharu
M
D003902:Detergents; D004530:Egg Yolk; D005960:Glucosides; D008081:Liposomes; D008560:Membrane Fluidity; D008823:Micelles; D010316:Particle Size; D010713:Phosphatidylcholines; D022161:Transport Vesicles / Q000502:physiology*
D003902:Detergents; D005960:Glucosides; D008081:Liposomes; D008823:Micelles; D010713:Phosphatidylcholines; C018619:octyl-beta-D-glucoside