Göran Lindblom

Orientation and mobility of molecules in membranes studied by polarized light spectroscopy.

Biological membranes are composed of mainly lipids and proteins. The physical properties of the lipids, forming a bilayer structure, are of crucial importance for the living cell, since the plasma membrane is the guardian barrier towards the environment. Thus, the functioning cell needs a highly stable lipid bilayer, which depends on molecular packing and orientation properties of the various membrane components (Wieslander et al. 1980). The spatial arrangement of the membrane proteins incorporated in the lipid matrix plays an essential role for the different chemical processes occurring at or within the membrane. Information about molecular orientation and mobility is therefore necessary for unravelling the functional mechanisms of a biological membrane.

Proton NMR bandshape studies of lamellar liquid crystals and gel phases containing lecithins and cholesterol

Proton NMR spectra for gel and liquid crystalline samples, composed of dimyristoyl and/or dipalmitoyl lecithin, cholesterol and water, can be consistently interpreted in terms of mesophase symmetry and molecular diffusion according to a model proposed by Wennerstrom (Wennerstrom, H. (1973) Chem. Phys. Lett. 18, 41-44). It is shown by computer simulation that the characteristic super-lorentzian bandshape of the lamellar mesophase can be described by the superposition of three gaussian curves. The NMR signal of the gel phase can be simulated by the superposition of two gaussian curves with widths at half height of 2.5 kHz and 19 kHz. An upper limit of the lateral diffusion coefficient of the lecithin molecules in the gel phase is calculated to be about 5-10(-15) m-2/s. It is therefore concluded that the static intermolecular dipolar couplings average to zero in the lamellar mesophase. An estimation of the order parameter of the liquid crystalline phase is made from experimental data and a calculated rigid lattice linewidth. A two phase system is shown to exist in the temperature range 28-34 degrees C for a mesophase of a mixture of dimyristoyl and dipalmitoyl lecithin. The presence of cholesterol results in enhanced lateral diffusion of the lecithin molecules at temperatures below the Chapman transition point.

Effects of anesthetics on water permeability and lipid metabolism in acholeplasma laidlawii membranes

The addition of tetracaine and diethyl ether to Acholeplasma laidlawii at concentrations commonly used for local anesthesia did not affect water permeability over the cell membrane, as measured by a pulsed magnetic field gradient NMR method. However, A. laidlawii changed its membrane lipid composition upon treatment with these anesthetics. Both tetracaine and diethyl ether addition resulted in a decrease in the molar ratio between the major membrane glucolipids, monoglucosyldiacylglycerol and diglucosyldiacylglycerol. The ratio between saturated and unsaturated acyl chains did not change. The results are in accordance with our proposal that A. laidlawii regulates its lipid composition in order to maintain optimal packing stability in the membrane (Wieslander, A., Christiansson, A., Rilfors. L. and Lindblom, G. (1980) Biochemistry 19, 3650--3655). Introduction of anesthetics into the hydrophobic region of a bilayer is likely to affect the lipid packing. A membrane which contains lipids like monoglucosyldiacylglycerol, which forms a reversed hexagonal phase, will be destabilized unless the amounts of such lipids are reduced. The membrane concentration of anesthetics was estimated to one molecule per 12--15 lipid molecules. The fact that A. laidlawii regulates its lipid composition as a response to these concentrations, despite their negligible effect on water permeability, indicates a high sensitivity of this regulatory system.

MOLECULAR AMPHIPHILE BILAYERS FORMING A CUBIC PHASE IN AMPHIPHILE-WATER SYSTEMS

ABSTRACT Structural properties are discussed of the cubic phase in monoglyceride-water systems, which is proposed to consist of a continuous lipid bilayer separating two not connected water channel systems. This cubic phase can solubilize large amounts of other lipids, such as cholesterol and lecithin, and a hydrophobic protein, A-gliadin. The same type of cubic phase occurs also in galacto-lipid systems and in systems of lysolecithin. The biological significance of this phase is discussed, and a general mechanism for fusion of cell membranes or liposomes based on a lamellar -- cubic transition is proposed.

The Structure of a Lyotropic Liquid Crystalline Phase that Orients in a Magnetic Field

Abstract The structure of a lyotropic liquid crystalline phase with positive diamagnetic anisotropy (type I), that spontaneously orients in a magnetic field has been studied by means of water NMR quadrupole splittings, NMR diffusion and polarized absorption spectroscopy. It is concluded that this phase is built up of long rodlike aggregates. A preliminary study of a sample with negative diamagnetic anisotropy (type II) shows that this phase probably consists of lamellar aggregates. It is suggested that these phases are suitable as orientation matrices for studies of chromophores with polarized light spectroscopy.

Fluorescence detected linear dichroism. A new method for studies of molecular orientation in uniaxial systems

A theoretical and experimental description of a new light spectroscopic method for determination of second rank order parameters is presented. The linear dichroism is obtained from the total fluorescent intensity, measured by using an integrating sphere. The method has been tested on a dichroic sample consisting of a stretched polymer film with an incorporated dye (2,2′‐diethyl thiocarbocyanide iodide). The main advantages of using emitted light are the high sensitivity and selectivity. With the method described the molecular orientation of a fluorophore in a mixture of other absorbing chromophores may be studied. It is also suggested that the integrating sphere should be used in determinations of excitation spectra and for measurements of fluorescence detected circular dichroism.

Molecular and Ionic Behaviour at Water-Amphiphile Interfaces

In systems containing aggregates of amphiphilic compounds there is a spatial separation between the hydrocarbon chains and the water molecules. The decisive feature is the interface betwen the two distinctly different regions and to examine, for example, the energetic and kinetic conditions for the formation of various amphiphilic aggregates a prerequisite is information on molecular interactions and dynamic events in the interface region. While the hydrophobic interaction, although not understood in detail, can be accounted for rather well semiempirically, our understanding of the interactions in the polar part is deficient. A factor of almost 100 higher c.m.c. of ionic than of non-ionic surfactants may be given as a single example of the importance of the interactions in the polar part of the amphiphile.