Phase behavior of the major lipids of tetrahymena ciliary membranes

A lipid-phase separation model of low-temperature damage to biological membranes

An hypothesis is proposed to explain the damage caused to biological membranes exposed to low temperatures. The thesis rests on the general observation that the lipid components of most membranes are heterogeneous and undergo phase transitions from gel-phase lamellae to liquid-crystalline lamellae and some to a non-lamellar, hexagonal-II phase over a wide range of temperatures. As a consequence of these phase transitions the lateral distribution of the lipids characteristic of the growth temperature is disturbed and redistribution takes place on the basis of the temperature at which phase transitions occur. When membranes are cooled, first the non-lamellar forming lipids pass through a transition to a fluid lamellar phase and are miscible with bilayer-forming lipids into which they diffuse. On further cooling the high-melting-point lipids begin to crystallize and separate into a lamellar gel phase, in the process excluding the low-melting point lipids and intrinsic proteins. The lipids in these remaining regions form a gel phase at the lowest temperature. It is suggested that, because the non-lamellar lipids tend to undergo a liquid-crystalline to gel-phase transition at higher temperatures than lamellar-forming lipids, these will tend to phase separate into a gel phase domain rich in these lipids. Damage results when the membrane is reheated, whereupon the hexagonal-II-forming lipids give rise to non-lamellar structures. These probably take the form of inverted micelles sandwiched within the lipid bilayer and they completely destroy the permeability barrier properties of the membrane. The model is consistent with the phase behavior of membrane lipids and the action of cryoprotective agents in modifying lipid phase properties.

Cation-dependent segregation phenomena and phase behavior in model membrane systems containing phosphatidylserine: influence of cholesterol and acyl chain composition

The addition of Ca2+ to model membrane systems containing phosphatidylserine (PS) can have remarkable effects on the distribution of PS and the overall polymorphic phase [bilayer or hexagonal (HII)] assumed by the lipid mixture. In this study, we examine the influence of Ca2+ on lipid mixtures composed of well-defined (synthetic) species of PS, phosphatidylethanolamine (PE), and phosphatidylcholine (PC) in the presence and absence of cholesterol by employing 31P and 2H NMR, freeze-fracture, and X-ray techniques. It is shown that whereas Ca2+ can segregate PS into crystalline cochleate domains in equimolar mixtures of dioleoyl-PE and dioleoyl-PS (DOPS), such effects are not observed for mixtures containing more unsaturated (dilinoleoyl) species of PS. The addition of cholesterol to these PE-PS systems inhibits Ca2+-induced segregation of DOPS and facilitates Ca2+-triggered hexagonal (HII) phase formation for both the PE and the PS components. In contrast, in equimolar mixtures of DOPS with dioleoyl-PC, Ca2+-induced segregation of phospholipid is not affected by the presence of up to 33 mol % cholesterol. These and related effects suggest that, in multicomponent biomembrane systems containing both PE and cholesterol, phase segregation of PS by Ca2+ may not be readily achievable. These results are discussed with regard to the reliability of 31P NMR phase identifications of phospholipid structure in model and biological membranes and demonstrate that in mixed lipid systems the influence of divalent cations on lipid distribution and structure can be exquisitely sensitive to details of the local lipid composition.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of growth temperature on the membrane lipid environment of the psychrophilic bacterium Micrococcus cryophilus

The relationship between the delta 9-desaturase activity of the psychrophilic bacterium Micrococcus cryophilus grown at different temperatures and the physical state of its membrane lipids as measured by ESR spectroscopy has been studied. Arrhenius plots of desaturase activity were biphasic with a discontinuity at a temperature which depended upon the bacterial growth temperature. Changes in the desaturase activation energy, which increased as the growth temperature was lowered, are discussed in the context of membrane lipid fluidity adaptation to changing environmental temperature. The fluidity of membranes and isolated lipids was measured using nitroxide-labeled fatty acids. The spectra of 2-(10-carboxydecyl)-2-hexyl-4,4-dimethyl-3-oxazolidinoxyl in membranes indicated that there were two lipid environments within the membrane whose relative proportions were dependent both on temperature of measurement and on bacterial growth temperature. In contrast, 2-(3-carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinoxyl spectra showed a single lipid environment and plots of log order parameter (S3) vs 1/T were biphasic with inflexion temperatures which were closely related to the bacterial growth temperature. As with membranes, plots of log S3 vs 1/T for total lipids, phosphatidylglycerol and cardiolipin, but not phosphatidylethanolamine, were biphasic and showed inflexions which correlated well with bacterial growth temperature. These results are interpreted as being consistent with a location for the desaturase within the bulk lipid of the membrane rather than in association with specific lipid types.

An X-ray diffraction study on phase transition temperatures of various membranes isolated from Tetrahymena pyriformis cells grown at different temperatures

Mitochondrial, microsomal and pellicular membranes were isolated from Tetrahymena cells grown at 39 degrees C or 15 degrees C, and phospholipids, in turn, were separated from total lipids extracted from these membranes. The effect of growth temperature on their solid-to-fluid phase transition temperature was examined by wide-angle X-ray diffraction. The transition temperatures of phospholipids from mitochondria, microsomes and pellicles were 21, 19 and 26 degrees C for cells grown at 39 degrees C and -8, -3 and 6 degrees C for cells grown at 15 degrees C, respectively. All phospholipids were found in a completely fluid state at these growth temperatures. From a comparison between the phospholipids and total lipids from pellicles of cells grown at 39 degrees C, a triterpenoid alcohol, tetrahymanol, caused the transition temperature to increase. The alignment of tetrahymanol in membranes was examined with pellicle'a total lipid oriented in a sample holder.