Bilayer membranes extended

I would like to extend Prof. Simon s characterizations of these beautiful new molecules to include a description of the effects on lipid bilayers of his Na+ selective compound number 11, which my post-doctoral student, Kun-Hung Kuo, and I have found to induce an Na+ selective permeation across lipid bilayer membranes [K.-H. Kuo and G. Eisenman, Naf Selective Permeation of Lipid Bilayers, mediated by a Neutral Ionophore, Abstracts 21st Nat. Biophysical Society meeting (Biophys. J., 17, 212a (1977))]. This is the first example, to my knowledge, of the successful reconstitution of an Na+ selective permeation in an artificial bilayer system. (Presumably the previous failure of such well known lipophilic, Na+ complexing molecules as antamanide, perhydroan-tamanide, or Lehn s cryptates to render bilayers selectively permeable to Na+ is due to kinetic limitations on their rate of complexation and decomplexation). 

The endoplasmic reticulum (ER) is composed of flattened sacs and tubes of membranous bilayers that extend throughout the cytoplasm enclosing a large intracellular space. The luminal space (Fig. 1-5) is continuous with the outer membrane of the nuclear envelope (Fig. 1-10). It is involved in the synthesis of proteins and their transport to the cytoplasmic membrane (via vesicles, small spherical particles with an outer bilayer membrane). The rough ER (RER) has flattened stacks of membrane that are studded on the outer (cytoplasmic) face with ribosomes (discussed later in this section) that... 

D Correlation Spectroscopy. A simple, quahtative approach has been described for the determination of membrane protein secondary structure and topology in lipid bilayer membranes." The new approach is based on the observation of wheel-like resonance patterns in the NMR H- N/ N polarization inversion with spin exchange at the magic angle (PISEMA) and H/ N HETCOR spectra of membrane proteins in oriented lipid bilayers. These patterns, named Pisa wheels, have been previously shown to reflect helical wheel projections of residues that are characteristic of a-helices associated with membranes. This study extends the analysis of these patterns to P-strands associated with membranes and demonstrates that, as for the case of a-helices, Pisa wheels are extremely sensitive to the tilt, rotation, and twist of P-strands in the membrane and provide a sensitive, visually accessible, qualitative index of membrane protein secondary structure and topology. 

At frequencies below 63 Hz, the double-layer capacitance began to dominate the overall impedance of the membrane electrode. The electric potential profile of a bilayer membrane consists of a hydrocarbon core layer and an electrical double layer (49). The dipolar potential, which originates from the lipid bilayer head-group zone and the incorporated protein, partially controls transmembrane ion transport. The model equivalent circuit presented here accounts for the response as a function of frequency of both the hydrocarbon core layer and the double layer at the membrane-water interface. The value of Cdl from the best curve fit for the membrane-coated electrode is lower than that for the bare PtO interface. For the membrane-coated electrode, the model gives a polarization resistance, of 80 kfl compared with 5 kfl for the bare PtO electrode. Formation of the lipid membrane creates a dipolar potential at the interface that results in higher Rdl. The incorporated rhodopsin may also extend the double layer, which makes the layer more diffuse and, therefore, decreases C. ... 

In schistosomes the tegument is about 4 /im thick. It is limited externally by a heptalaminate membrane that consists of two closely apposed lipid bilayers. Based on the distribution of intramembranous particles observed in freeze-fracture studies, the inner bilayer is the true plasma membrane of the parasite. The membrane extends inward 1-2 pm along numerous pits that branch and interconnect to form a lattice which increases the surface area of the parasite at least 10-fold (28). The tegument of... 

Kimizuka and coworkers have extended their own work, to the assembly of bilayer membranes. For example, multiple hydrogen-bonding interactions between 57 and cyanuric acid derivative 59 containing a polar head group leads to hydrogen-bonded tapes that organize into bilayers [115,116]. The proposed supramolecular structure of the bilayer, represented schematically in Figure 34, was verified by IR and x-ray diffraction studies of films cast from an aqueous dispersion of the bilayer, as well as by electron microscopy of the dispersions. 

In facilitated transport, proteins that extend from one side of the bilayer membrane to the other provide a channel through which certain substances can diffuse more rapidly than by passive diffusion to meet cellular needs. These protein channels allow transport of chloride ion (Cr), bicarbonate ion (HCO3 ), and glucose molecules in and out of the cell. 

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