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Phospholipids thermotropic phase transitions

Papahajopoulos, D., M. Moscarello, E.H. Eylar, and T. Isac. 1975. Effects of proteins on thermotropic phase transitions of phospholipid membranes. Biochim Biophys Acta 401 317-335. [Pg.380]

A DSC heating scan of a fully hydrated aqueous dispersion of dipalmitoylphosphatidylcholine (DPPC), which has been annealed at 0°C for 3.5 days, is displayed in Fig. 2. The sample exhibits three endothermic transitions, termed (in order of increasing temperature) the subtransition, pretransition, and main phase transition. The thermodynamic parameters associated with each of these lipid phase transitions are presented in Table 1. The presence of three discrete thermotropic phase transitions indicates that four different phases can exist in aimealed, fully hydrated bilayers of this phospholipid, depending on temperature and thermal history. All of these phases are lamellar or bilayer phases differing only in their degree of organization. [Pg.129]

An illustration of a lipid-water phase diagram, in which the transitions are driven by water content, is shown in Fig. 2 (43). A similar phase sequence can be produced by changes in temperature as well, and phospholipid phase diagrams generally exhibit pronounced temperature dependence. A generalized phase sequence of thermotropic phase transitions for the typical membrane lipids can be defined (44) ... [Pg.895]

The thermotropic phase transition temperature of a vesicle composed of a mixture of dipalmitoyl and dimyristoyl phosphatidylcholine (DPPC and DMPC, respectively) is intermediate between the phase transition temperatures of the single lipid vesicles and reflects the relative concentrations of the two lipids in the vesicle. This can be used to determine the rate of exchange of phosphatidylcholine between two unilamellar vesicles of initially pure phospholipid. [Pg.216]

Most of the diffraction work with synchrotron on membranes done up to now can be grouped into one of the following two categories Firstly, studies on thermotropic phase transitions of phospholipid model systems. These investigations are aimed at the kinetics and structural mechanisms of the transitions, and are beginning to close the gap between the wealth of existing data from spectroscopic techniques, with their inherent time resolution and the detailed structural data from static X-ray diffraction. [Pg.187]

Fully hydrated bilayers composed of a single phospholipid species undergo a well-defined thermotropic phase transition (see Fig. 2.1) in which the lipid chains change from an ordered, pseudocrystalline or gel state to a fluid or liquid crystalline state which is similar to that found in biological membranes. The lipid chain configuration in the high-temperature, fluid phase is that described in the final section of the previous chapter. In the low temperature, ordered phase, the chains are essentially in the parallel, all-trans state,and may be tilted relative to the bilayer normal, the state as in phosphatidylcholines, or untilted the Lq state as in phosphatidylethanolamines. Additionally, an inter-... [Pg.148]

The existence of phospholipid bilayers in biological membranes has since been well established by numerous experimental data using newly improved methods. Melchior and Steim (1976) have observed thermotropic phase transitions in membrane lipids and have postulated that these transitions come from a melting of hydrocarbon chains associated with one another. While lipids might exist in one of several liquid-crystalline phases, the physical data indicate that a bilayer is the most probable configuration. Other physical data, obtained by differential thermal analysis, NMR spectroscopy. X-ray diffraction, and light microscopy, support the view that the reversible thermotropic-gel-liq-uid-crystal phase transition arises from the melting of the hydrocarbon interiors of lipid bilayers (Chapman, 1970 Oseroff et al., 1973). [Pg.381]

In addition to this thermotropic mesomorphism, a lysotropic mesomorphism is observed [98]. The phase transition temperature, Tt, for the transition from the crystalline to the liquid crystalline state decreases as a function of water content. The decrease in Ttis due to destabilization of the crystal lattice in the head group region by water molecules. This, in turn, decreases the interaction between the fatty acid chains. When the water content reaches a certain level, the phospholipids assume a thermodynamically optimal arrangements whereby the fatty acids are directed to the... [Pg.22]

Although studies of the thermotropic phase behavior of singlecomponent multilamellar phospholipid vesicles are necessary and valuable, these systems are not realistic models for biological membranes that normally contain at least several different types of phospholipids and a variety of fatty acyl chains. As a first step toward understanding the interactions of both the polar and apolar portions of different lipids in mixtures, DSC studies of various binary and ternary phospholipid systems have been carried out. Phase diagrams can be constructed by specifying the onset and completion temperatures for the phase transition of a series of mixtures and by an inspection of the shapes of the calorimetric traces. A comparison of the observed transition curves with the theoretical curves supports... [Pg.130]

The occurrence of cholesterol and related sterols in the membranes of eukaryotic cells has prompted many investigations of the effect of cholesterol on the thermotropic phase behavior of phospholipids (see References 23-25). Studies using calorimetric and other physical techniques have established that cholesterol can have profound effects on the physical properties of phospholipid bilayers and plays an important role in controlling the fluidity of biological membranes. Cholesterol induces an intermediate state in phospholipid molecules with which it interacts and, thus, increases the fluidity of the hydrocarbon chains below and decreases the fluidity above the gel-to-liquid-crystalline phase transition temperature. The reader should consult some recent reviews for a more detailed treatment of cholesterol incorporation on the structure and organization of lipid bilayers (23-25). [Pg.130]

The major transition in membranes of log-phase cells is the broad gel to liquid-ciys-talline transition of the phospholipids that begins below 0 °C and ends at 20-24 °C. While observing the thermotropic transitions in bacterial membranes at stages of cell... [Pg.64]

Recently it was shown (2) that when a fully saturated phospholipid is heated, a marked change takes place in the appearance of the infrared spectrum, corresponding to a transition from a crystalline to a liquid crystalline phase, many tens of degrees below the reported capillary melting point. Phospholipids therefore exhibit thermotropic mesomorphism. In this paper we discuss the results obtained by other techniques which we have been using in our laboratory for the study of phospholipids. [Pg.165]

Thermotropic behavior of phospholipids in the presence of blood clotting factors. The changes in the transition temperature (Tm) of phospholipid mixtures induced by the presence of the proteins were monitored by fluorescence polarization of the hydrophobic probe, DPH, inserted in the bilayers. These changes are generally interpreted as indicative of phase separation, as already demonstrated for the effect of calcium, at concentrations higher than 10 mM in PS-rich bilayers (23), and in the case of some proteins (24). [Pg.188]


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See also in sourсe #XX -- [ Pg.147 ]




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