Modification of Lipid Phase Behavior with Membrane-Bound Cryoprotectants

摘要

Several derivatives of cholesterol containing oxyethylene headgroups with and without a terminal galactose have been synthesized in order to examine the effects of immobilizing a cryoprotectant at a membrane surface. In this work, we have studied the ability of the triethoxycholesterol (TEC) and triethoxycholesterol galactose (TEC-Gal) derivatives to modulate the phase behavior of phosphatidylcholine and phosphatidylethanolamine membranes. Methods of fluorescence polarization, Phosphorus 31-Nuclear magnetic resonance and freeze-fracture electron microscopy were employed to monitor these changes in lipid phase behavior. Fluorescence polarization data demonstrated the ability of the derivatives to fluidize gel state and rigidify liquid-crystalline state phosphatidylcholines in a manner similar to that observed for cholesterol. Unlike cholesterol, however, the T sub m. of dipalmitoylphospatidylcholine (DPPC) was reduced in a concentration-dependent manner with each of the derivatives. Freeze-fracture electron microscopy and 31 P-NMR of (dioleoylphosphatidylethanolamine) dispersions indicate an increase in the lamellar to hexagonal phase-transition temperature on the order of 10-20 C above room temperature for mixtures with 20 mol% of the derivatives. These results are discussed in terms of the properties exhibited by compounds such as carbohydrates, which are known to serve as cryoprotectants for synthetic and biological membranes. keywords: Cryopreservation, Phospholipids, Reprints. (aw)