title: Dehydration-induced lamellar-to-hexagonal-II phase transitions in DOPE/DOPC mixtures.
abstract: Plasma membranes of protoplasts isolated from non-acclimated rye plants undergo a transition from the bilayer to the inverted hexagonal (HII) phase during freeze-induced dehydration at -10 degrees C. It has been suggested (Bryant, G. and Wolfe, J. (1989) Eur. Biophys. J. 16, 369-372) that the differential hydration of various membrane components may induce fluid-fluid demixing of highly hydrated (e.g., PC) from poorly hydrated (PE) components during dehydration. This could yield a PE-enriched domain more prone to form the HII phase. We have examined the lyotropic phase behavior of mixtures of DOPE and DOPC at 20 degrees C by freeze-fracture electron microscopy, differential scanning calorimetry, and X-ray diffraction. HII phase formation was favored by higher proportions of DOPE and lower water contents. Mixtures of 1:1 and 1:3 DOPE/DOPC had a hydration-dependent appearance of two L alpha phases at water contents just above those at which the HII phase occurred. The hydration-dependence of the lamellar repeat spacings suggested that the DOPE-enriched domains preferentially underwent the L alpha-to-HII phase transition. Mixtures of 3:1 DOPE/DOPC did not separate into two L alpha phases during dehydration. These data suggest that the differential hydration characteristics of various membrane components may induce their lateral fluid-fluid demixing during dehydration.
authors.affiliation: Department of Soil, Crop and Atmospheric Sciences, Cornell University, Ithaca, NY 14853.
authors.forename: M S
authors.initials: MS
authors.lastname: Webb
authors.forename: S W
authors.initials: SW
authors.lastname: Hui
authors.forename: P L
authors.initials: PL
authors.lastname: Steponkus
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005614:Freeze Fracturing; D010713:Phosphatidylcholines / Q000737:chemistry*; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D011523:Protoplasts / Q000737:chemistry*; D012434:Secale; D014867:Water
chemical_list: D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D014867:Water; C020888:1,2-dielaidoylphosphatidylethanolamine; C017251:1,2-oleoylphosphatidylcholine