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  • 1
    Electronic Resource
    Electronic Resource
    Local dielectric properties around polar region of lipid bilayer membranes (1985)
    Springer
    The journal of membrane biology 85 (1985), S. 225-231 
    Details
    ISSN: 1432-1424
    Keywords: dielectric constant ; fluorescence study ; liposomes ; calcium effect ; phase transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Local dielectric constant was evaluated from the Stokes shifts of fluorescence spectra ofl-α-dansylphosphatidylethanolamine (DPE) incorporated into liposomes made of synthetic phosphatidylcholine (dipalmitoyl or distearoyl) or bovine brain phosphatidylserine. The evaluation was established as follows. First, the Stokes shift of DPE was assured to follow Mataga-Lippert's equation and was a function of the dielectric constant and the refractive index in some standard organic solvents. Second, the change of the refractive index did not contribute much to the change in the Stokes shift. Third, the time resolved fluorescence depolarization of DPE in liposomes showed that the cone wobbling diffusion was rapid relative to the fluorescence lifetime and therefore that the dielectric relaxation did not affect the evaluation of the constant in the polar region of membranes. We then investigated the characteristics of the local dielectric constant in the polar region of the lipid bilayer and found that the dielectric constant varies between 4 and 34 depending upon calcium binding and also gel/liquid-crystal phase transition. Such large changes of the local dielectric constant were further correlated with the dynamic structure of lipid bilayer membranes measured by conventional fluorescence depolarization techniques. The large changes of dielectric constant around the polar region suggest that electrostatic interactions at this region can be altered 10-fold by such ionic or thermotropic factors and therefore that local dielectric properties can play crucial roles in membrane functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871517
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  • 2
    Electronic Resource
    Electronic Resource
    Phospholipase C and the physical states of polar head groups of lipids (1987)
    Springer
    The journal of membrane biology 96 (1987), S. 187-191 
    Details
    ISSN: 1432-1424
    Keywords: phospholipase C ; liposomes ; fluorescence study ; local dielectric property ; rotational freedom
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Activity of phospholipase C fromClostridium perfringens on liposomes made fromsn-3-phosphatidylcholine, dimyristoyl (DMPC), dipalmitoyl (DPPC) or distearoyl (DSPC) was measured at various temperatures and was correlated with their gel/liquid-crystalline phase transitions (T c : 23, 41.5, 52°C for DMPC, DPPC, DSPC, respectively). In all cases, the activity of phospholipase C was high in the gel phases of the substrates and was almost zero in their liquid-crystalline phases. Fluorescence depolarization measurements of N-dansyl-sn-3-phosphatidylethanolamine (DPE) and 1,6-diphenyl-1,3,5-hexatriene (DPH) incorporated into the liposomes showed that both the head group and the alkyl chains of the lipids were immobilized in the gel phases but were highly mobile in the liquid-crystalline phase. These results indicate that the rotational mobility of lipids (both of the head groups and the alkyl chains) was not a major factor in the phospholipase C reaction. It is inferred that some electrostatic and/or hydrophobic interactions might play important roles in regulation of the phospholipase C activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869244
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