Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: CAS:18194-24-6 (DMPC)
 1,152 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Changes in the thermal behavior of DMPC (dimyristoyl-L-phosphatidylcholine) and an equimolar mixture of DMPC and DMPE (dimyristoyl-L-phosphatidylethanolamine) induced by the plant hormone abscisic acid (ABA) have been investigated using fluorescent probes. The fluorescence decay of the hydrophobic probe 1,6-diphenyl-1,3,5-hexatriene (DPH) in these vesicles has been measured using frequency-domain fluorometry, and has been analyzed using both models of discrete exponential components and continuous lifetime distributions. In the DMPC vesicles, using the distributional approach, higher center and width values were observed in the presence of abscisic acid (ABA), indicating a decrease in the dielectric constant of the lipid phase that we attribute to a decrease in the water concentration within the bilayer. Moreover, the presence of ABA in the liposomes increased the phospholipid phase transition temperature. The addition of ABA to the DMPC/DMPE mixture strongly increased the microheterogeneity of the system as reported by the FWHM (full-width at half-maximum) of the distributional approach.
 ...
PMID:Abscisic acid-induced microheterogeneity in phospholipid vesicles. A fluorescence study. 213 48

A phenomenological model is proposed to describe the membrane phase equilibria in binary mixtures of saturated phospholipids with different acyl-chain lengths. The model is formulated in terms of thermodynamic and thermomechanic properties of the pure lipid bilayers, specifically the chain-melting transition temperature and enthalpy, the hydrophobic bilayer thickness, and the lateral area compressibility modulus. The model is studied using a regular solution theory made up of a set of interaction parameters which directly identify that part of the lipid-lipid interaction which is due to hydrophobic mismatch of saturated chains of different lengths. It is then found that there is effectively a single universal interaction parameter which, in the full composition range, describes the phase equilibria in mixtures of DMPC/DPPC, DPPC/DSPC, DMPC/DSPC, and DLPC/DSPC, in excellent agreement with experimental measurements. The model is used to predict the variation with temperature and composition of the specific heat, as well as of the average membrane thickness and area in each of the phases. Given the value of the universal interaction parameter, the model is then used to predict the phase diagrams of binary mixtures of phospholipids with different polar head groups, e.g., DPPC/DPPE, DMPC/DPPE and DMPE/DSPC. By comparison with experimental results for these mixtures, it is shown that difference in acyl-chain lengths gives the major contribution to deviation from ideal mixing. Application of the model to mixtures with non-saturated lipids is also discussed.
 ...
PMID:Modelling the phase equilibria in two-component membranes of phospholipids with different acyl-chain lengths. 317 84

Fourier transform infrared spectroscopy has been used to characterize the carbonyl stretching vibration of DMPC, DMPE, DMPG, and DMPA, all labeled with 13C at the carbonyl group of the sn-2 chain. Due to the vibrational isotope effect, the 13C = O and the 12C = O vibrational bands are separated by ca. 40-43 cm-1. This frequency difference does not change when the labeling is reversed with the 13C = O group at the sn-1 chain. For lipids in organic solvents possible conformational differences between the sn-1 and sn-2 ester groups have no effect on the vibrational frequency of the C = O groups. In aqueous dispersion unlabeled phospholipids always show a superposition of two bands for the C = O vibration located at ca. 1740 and 1727 cm-1. These two bands have previously been assigned to the sn-1 and sn-2 C = O groups. FT-IR spectra of 13C-labeled phospholipids show that the vibrational bands of both, the sn-1 as well as the sn-2 C = O group, are clearly superpositions of at least two underlying components of different frequency and intensity. Band frequencies were determined by Fourier self-deconvolution and second-derivative spectroscopy. The difference between the component bands is ca. 11-17 cm-1. Again, the conformational effect as shown by reversed labeling is negligible with only 1-2 cm-1. The splitting of the C = O vibrational bands in H2O and D2O is caused by hydrogen bonding of water molecules to both C = O groups as shown by a comparison with spectra of model ester compounds in different solvents. To extract quantitative information about changes in hydration, band profiles were stimulated with Gaussian-Lorentzian functions. The chemical nature of the head group and its electronic charge have distinctive effects on the extent of hydration of the carbonyl groups. In the gel and liquid-crystalline phase of DMPC the sn-2 C = O group is more hydrated than the sn-1 C = O. This is accord with the conformation determined by X-ray analysis. In DMPG the sn-1 C = O group seems to be more accessible to water, indicating a different conformation of the glycerol backbone.
 ...
PMID:Fourier transform infrared spectroscopy of 13C = O-labeled phospholipids hydrogen bonding to carbonyl groups. 323 7

Priest's phenomenological model (Mol. Cryst. Liq. Cryst. 60 (1980) 167.) on one- and two-component PC bilayers is extended here. We constructed a new excess free energy term in the state function to describe the thermodynamic properties of the two-component phospholipid bilayers where the chain lengths and the polar heads of the components can be different simultaneously. By means of this generalized state function, we can calculate the phase diagrams of DPPC/DPPE, DMPC/DMPE, DMPC/DPPE, DPPC/DMPE and DSPC/DMPE mixtures. We obtained complete miscibility both in the liquid crystalline and in the gel phase if the chain lengths of the components were the same. If the chain length of the PE component was longer than that of the PC component, we obtained a peritectic system. A eutectic system was obtained in the reverse case. The results of the model were compared with the experimental data available. Applying the quasichemical approximation, we determined the molecular meaning of the phenomenological model parameters. Namely, sigma and gamma are proportional to the sublimation heat of the CH2 group in the long-chain alkanes and to the hydrogen-bonding energy between the polar heads of the ethanolamines; otherwise the model resulted in--1.94 kcal/mol per CH2 for the sublimation heat and --1.4 kcal/mol for the hydrogen-bond energy.
 ...
PMID:Landau theory of two-component phospholipid bilayers. I. Phosphatidylcholine/phosphatidylethanolamine mixtures. 666 96

Surfactin, an acidic cyclic lipopeptide produced by strains of Bacillus subtilis, is a powerful biosurfactant possessing biological activities. Interactions of ionized surfactin (two negative charges) with lecithin vesicles have been monitored by changes in its CD spectra. These changes are more important in the presence of Ca2+ ions. We have studied the penetration of ionized surfactin into lipid monolayers. Using dimyristoyl phospholipids, the surfactin penetration is more important in DMPC than in DMPE monolayers and is greatly reduced in DMPA monolayers because of electrostatic repulsion. The surfactin penetration is lowered when the acyl chain length of the phospholipids increases. The exclusion pressure varies from 40 mN m-1 for DMPC to 30 mN m-1 for DPPC and 18 mN m-1 for egg lecithin. The presence of Ca2+ ions, which neutralize the charges of both surfactin and lipids in the subphase, leads to an important change of the penetration process that is enhanced in the case of acidic, but also of long chain (higher than C14) zwitterionic phospholipids (DPPC and lecithin). From compression isotherms of mixed surfactin/phospholipid monolayers, it appears that surfactin is completely miscible with phospholipids. The present study shows that surfactin penetrates spontaneously into lipid membranes by means of hydrophobic interactions. The insertion in the lipid membrane is accompanied by a conformation change of the peptide cycle.
 ...
PMID:Interactions of surfactin with membrane models. 761 35

Methylmercury (CH3Hg(II)) interactions with multilamellar vesicles of dimyristoyl(DM)- and dipalmitoyl(DP)-phosphatidylcholine (PC), -phosphatidic acid (PA), -phosphatidylglycerol (PG), -phosphatidylserine (PS) and -phosphatidylethanolamine (PE) have been investigated from the metal viewpoint by solution 199Hg-NMR and from the membrane side by diphenylhexatriene fluorescence polarization and solid state 31P-NMR. Results can be summarized as follows: (1) CH3Hg(II) strong binding to membranes results in a progressive decrease of the free CH3HgOH 199Hg-NMR isotropic signal and because of a slow exchange, in the NMR time scale, between free and bound methylmercury pools the lipid/water partition coefficients, K(lw), of the CH3HgOH species can be determined in the lamellar gel (fluid) phase. It is found: K(lw)(DMPC) approximately 2 +/- 2 (2 +/- 2); K(lw)(DMPE) approximately 7 +/- 3 (16 +/- 3); K(lw)(DMPG) = 170 +/- 10 (110 +/- 10); K(lw)(DMPS) = 930 +/- 50 (1250 +/- 60); K(lw)(DMPA) = 1250 +/- 60 (300 +/- 20). CH3Hg(II) interactions with membrane phospholipids are therefore electrostatic in nature and the phosphate moiety is proposed as a potential binding site. (2) The presence of CH3HgOH stabilizes the PG gel phase and destabilizes that of PS. No effect is observed on PC, PA and PE thermotropism. (3) methylmercury promotes the formation of isotropic 31P-NMR lines with PG, PA and PE systems suggesting the presence of non-bilayer phases and hence membrane reorganization. The above effects are compared to those of inorganic mercury Hg(II) and discussed in the context of cell toxicity.
 ...
PMID:Methyl mercury interactions with phospholipid membranes as reported by fluorescence, 31P and 199Hg NMR. 916 50

We have investigated the effect of lipids with phosphatidylethanolamine (PE) head groups on the stabilization of contacts between the tryptophan side chains of gramicidin and the lipid head groups. We initially developed two fluorescence methods that can be correlated to the spontaneous curvature of DOPC/DOPE and DOPC/DOPEme. One is based on bilayer structure and measures the rotational motion of a probe located close to the membrane surface relative to a more deeply-buried probe. The second is based on surface hydration/polarity and measures the emission energy of a polarity-sensitive probe located on the membrane surface. We used these methods to estimate the pseudo-curvature (i.e., curvature obtained by fluorescence measurements) of lipids with dimyristyl chains, and their pressure and temperature dependence. We then investigated the stability of gramicidin tryptophan-lipid contacts in DMPC/DMPE as a function of temperature and pressure. Stability was assessed by tryptophan rotational motion as determined by fluorescence anisotropy, since rotational motion is limited when the indoles are hydrogen bonded to the lipid head groups. The results suggest that the presence of PE lipids destabilizes these contacts due to either their smaller size relative to PC head groups, or their tendency to self-interact. Fluorescence quenching studies support these results.
 ...
PMID:Role of phosphatidylethanolamine lipids in the stabilization of protein-lipid contacts. 939 29

We have investigated the influence of the chemical structure and charge of the hydrophillic headgroup on the miscibility of saturated phospholipids with acyl chain lengths differing by two methylene units, namely DMPA/DPPA, DMPC/DPPC, DMPE/DPPE and DMPG/DPPG (0.1 M NaCl). All four mixtures were analysed by DSC at pH 7. To study the influence of a change in headgroup charge, we additionally investigated DMPA/DPPA mixtures at pH 4 and 12, and DMPG/DPPG mixtures at pH 2. The experimental DSC thermograms were fitted using methods described before [Johann et al., Biophys. J. 71 (1996), 3215-3228] to obtain the temperatures of onset and end of melting and first approximations for the non-ideality parameters as a function of composition. The resulting phase diagrams were then fitted using a four non-ideality parameter model for non-ideal, non-symmetric mixing in both phases. The phase diagram of the system DMPG/DPPG has a lens-like shape, the non-ideality parameters rhog and rhol for the gel and the liquid-crystalline phase, respectively, are zero, indicating ideal mixing in both phases. For the other mixtures, differences in miscibility are observed depending on the structure of the headgroup. At pH 7, rhog > rhol, i.e., the miscibility in the liquid-crystalline phase is more ideal than in the gel state. All rhog values are positive and the sequence for rhog observed is PA>PE>PC>PG. Partial protonation of PA at pH 4 or complete deprotonation at pH 12 leads to negative non-ideality parameters for both phases, indicating a preference for mixed pair formation. Protonation of PG in DMPG/DPPG mixtures at pH 2 leads to positive non-ideality parameters for both phases, indicating a tendency for demixing. The results show, that the miscibility of phospholipids with identical headgroups but chain lengths differing by two methylene groups is dependent on headgroup structure and on headgroup charge.
 ...
PMID:Miscibility of phospholipids with identical headgroups and acyl chain lengths differing by two methylene units: effects of headgroup structure and headgroup charge. 956 58

We report x-ray scattering, rheological, and freeze-fracture and polarizing microscopy studies of a liquid crystalline hydrogel called Lalpha,g. The hydrogel, found in DMPC, pentanol, water, and PEG-DMPE mixtures, differs from traditional hydrogels, which require high MW polymer, are disordered, and gel only at polymer concentrations exceeding an "overlap" concentration. In contrast, the Lalpha,g uses very low-molecular-weight polymer-lipids (1212, 2689, and 5817 g/mole), shows lamellar order, and requires a lower PEG-DMPE concentration to gel as water concentration increases. Significantly, the Lalpha,g contains fluid membranes, unlike Lbeta' gels, which gel via chain ordering. A recent model of gelation in Lalpha phases predicts that polymer-lipids both promote and stabilize defects; these defects, resisting shear in all directions, then produce elasticity. We compare our observations to this model, with particular attention to the dependence of gelation on the PEG MW used. We also use x-ray lineshape analysis of scattering from samples spanning the fluid-gel transition to obtain the elasticity coefficients kappa and B; this analysis demonstrates that although B in particular depends strongly on PEG-DMPE concentration, gelation is uncorrelated to changes in membrane elasticity.
 ...
PMID:The influence of polymer molecular weight in lamellar gels based on PEG-lipids. 964 87

Giant unilamellar vesicles (GUVs) composed of different phospholipid binary mixtures were studied at different temperatures, by a method combining the sectioning capability of the two-photon excitation fluorescence microscope and the partition and spectral properties of 6-dodecanoyl-2-dimethylamino-naphthalene (Laurdan) and Lissamine rhodamine B 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (N-Rh-DPPE). We analyzed and compared fluorescence images of GUVs composed of 1,2-dilauroyl-sn-glycero-3-phosphocholine/1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DLPC/DPPC), 1, 2-dilauroyl-sn-glycero-3-phosphocholine/1, 2-distearoyl-sn-glycero-3-phosphocholine (DLPC/DSPC), 1, 2-dilauroyl-sn-glycero-3-phosphocholine/1, 2-diarachidoyl-sn-glycero-3-phosphocholine (DLPC/DAPC), 1, 2-dimyristoyl-sn-glycero-3-phosphocholine/1, 2-distearoyl-sn-glycero-3-phosphocholine (DMPC/DSPC) (1:1 mol/mol in all cases), and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine/1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPE/DMPC) (7:3 mol/mol) at temperatures corresponding to the fluid phase and the fluid-solid phase coexistence. In addition, we studied the solid-solid temperature regime for the DMPC/DSPC and DMPE/DMPC mixtures. From the Laurdan intensity images the generalized polarization function (GP) was calculated at different temperatures to characterize the phase state of the lipid domains. We found a homogeneous fluorescence distribution in the GUV images at temperatures corresponding to the fluid region for all of the lipid mixtures. At temperatures corresponding to phase coexistence we observed concurrent fluid and solid domains in the GUVs independent of the lipid mixture. In all cases the lipid solid domains expanded and migrated around the vesicle surface as we decreased the temperature. The migration of the solid domains decreased dramatically at temperatures close to the solid-fluid-->solid phase transition. For the DLPC-containing mixtures, the solid domains showed line, quasicircular, and dendritic shapes as the difference in the hydrophobic chain length between the components of the binary mixture increases. In addition, for the saturated PC-containing mixtures, we found a linear relationship between the GP values for the fluid and solid domains and the difference between the hydrophobic chain length of the binary mixture components. Specifically, at the phase coexistence temperature region the difference in the GP values, associated with the fluid and solid domains, increases as the difference in the chain length of the binary mixture component increases. This last finding suggests that in the solid-phase domains, the local concentration of the low melting temperature phospholipid component increases as the hydrophobic mismatch decreases. At the phase coexistence temperature regime and based on the Laurdan GP data, we observe that when the hydrophobic mismatch is 8 (DLPC/DAPC), the concentration of the low melting temperature phospholipid component in the solid domains is negligible. This last observation extends to the saturated PE/PC mixtures at the phase coexistence temperature range. For the DMPC/DSPC we found that the nonfluorescent solid regions gradually disappear in the solid temperature regime of the phase diagram, suggesting lipid miscibility. This last result is in contrast with that found for DMPE/DMPC mixtures, where the solid domains remain on the GUV surface at temperatures corresponding to that of the solid region. In all cases the solid domains span the inner and outer leaflets of the membrane, suggesting a strong coupling between the inner and outer monolayers of the lipid membrane. This last finding extends previous observations of GUVs composed of DPPE/DPPC and DLPC/DPPC mixtures (, Biophys. J. 78:290-305).
 ...
PMID:A correlation between lipid domain shape and binary phospholipid mixture composition in free standing bilayers: A two-photon fluorescence microscopy study. 1086 69


1 2 3 4 Next >>