Transport through lipid bilayer membranes

Gutknecht, J. (1981). Inorganic mercury (Hg2+) transport through lipid bilayer membranes, J. Membrane Biol., 61, 61-66. 

Benz. R. Alkali ion transport through lipid bilayer membranes mediated by enniatin A and B and beauvericin. J. Membr. Biol. 1978, 43. 367- 394. 

Dimeric j8-cyclodextrin complexes have been used as model compounds to study membrane diffusion transport through lipid bilayer membranes. a-Cyclodextrin is able to interact with some optically-active benzene derivatives. The ability of the compound with the benzene ring to be inserted into the central cavity of the a-cyclodextrin molecule provided the driving force for complex formation. The effect of cyclodextrins on the dissociation of some azo dyes showed that the apparent Ka values of the dyes increased with increasing cyclodextrin concentration. The effect was explained as a hydrophobic interaction between the dye and the cyclodextrin molecules. 

Sugar Transport Through Lipid Bilayer Membranes. 

Gutnecht J, Walter A (1982) SCN and HSCN transport through lipid bilayer membranes a model for SCN" inhibition of gastric acid secretion. Biochim Biophys Acta 685 233-240... 

Gutknecht JJ (1981) Inorganic mercury transport through lipid bilayer membranes. Membr Biol 61 61... 

P. C. Jordan, Current Noise in Transport of Hydrophobic Ions Through Lipid Bilayer Membranes Including Diffusion Polarization in the Aqueous Phase, Biophys. Chem. 12, 1-11 (1980). 

Benz, R., Frohlich, 0. and Lauger, P. Influence of membrane structure on the kinetics of carrier-mediated ion transport through lipid bilayers. Biochem Biophys Acta 464 465-481, 1977. 

Molecules that cannot pass freely through the lipid bilayer membrane by themselves do so in association with carrier proteins. This involves two processes— facilitated dififrision and active transport—and highly specific transport systems. 

Transport and Cell Penetration. One of the causes of bacterial resistance to the cephalosporins is poor transport of the antibiotic through tlie outer membrane of gram-negative bacteria. This lipid-bilayer membrane carries receptor proteins for the recognition and transport of essential nutrients, but provides an effective barrier to large molecules. In the case of the cephalosporins there can be a considerable difference between the concentration required to inhibit intact cells and the concentrations required to saturate the target enzymes in broken cell piepaiations. 

The Si transporting proteins (structures of which are deduced from the cloned DNA sequences) are closely related in structure to other, well-characterized ion transporters14. They contain 12 a-helical transmembrane domains that fold to form a cylindrical channel— assembled like staves of a barrel — through the lipid bilayer membrane of the cell. However, the evidence suggesting an ion-type transporter needs to be resolved with results of recent physiological analyses of the pH-dependence of silicon uptake, suggesting that many diatom species most efficiently take up the unionized, neutral silicic acid16. 

From studies of lipid-water mixtures and isolated membranes the general functional features of the bilayer are known barrier properties, lateral diffusion, acyl chain disorder and protein association. To vmderstand the mechanisms behind a wide spectrum of membrane functions, a detailed picture at the level of local curvature is needed. Examples are fusion processes, cooperativity in receptor/ligand binding or transport through the bilayer of the proteins that are constantly synthesised for export from the endoplasmic reticulum. Some preliminary discussions of the possibilities of curved, rather than flat, membremes follow. 

The most general water transport mechanism is diffusion through lipid bilayers, with a permeability coefficient of 2-5 x 10 4 cm/sec. The diffusion through lipid bilayers depends on lipid structure and the presence of sterol (Subczyhski et al., 1994). It is suggested that the lateral diffusion of the lipid molecules and the water diffusion through the membrane is a single process (Haines, 1994). 

Fig. 18. Mechanism of carrier-mediated ion transport through a lipid bilayer membrane [Reproduced from Stark, G., et.al Biophys. j. 11, 981 (1971) and Benz, R., Stark, G. Biochem. Biophys. Acta 382 (1), 27 (1975).]...

Active transport is more valid for Cd and Cu, while passive uptake through the lipid bilayer membrane is valid for Ag and Hg (Langston and Bryan 1984). 

Many molecules do not diffuse through lipid bilayers (see Figure 5.6 and notice that sucrose and ions do not permeate). One of the most important functions of accessory molecules in the membrane is regulation of transport of molecules that do not pass freely through the lipid bilayer. Several classes of accessory molecules are engaged in membrane transport, as described in the sections that follow. 

In contrast to lipid bilayer membranes, it has been found [4] that the permeability coefficient of the human red-cell membrane to water did not change when the free cholesterol content in the membrane was varied from 0.84 to 1.87 mg/ml cells. Furthermore, the permeability of the human red-cell membrane to sulfate and some nonelectrolytes remained constant when membrane cholesterol was partially removed (for review, see [6]). These results, however, should not be taken as evidence that water transport in human red cells is independent of membrane cholesterol, since this degree of variation may be insufficient to produce alteration. In fact, extensive depletion of membrane cholesterol induces a marked increase in nonelectrolyte permeability. The effect of membrane cholesterol on the transport of water is also found in other membrane systems. For example, the polyene antibiotic. Amphotericin B, which interacts specifically with sterol-containing membranes, increases the permeability of the mucosal but not the serosal membrane of toad bladder to water and other solutes [32]. It is possible that membrane cholesterol only effects the movements through the lipid bilayer pathway. This may explain the findings that the permeabiUty coefficient of the human red cell membrane to water... 

Electrokinetic Flow and Ion Transport in Nanochannels, Fig. 3 Molecular model showing a single strand of poly(dC) DNA passing through an a-hemolysin protein pore in a lipid bilayer membrane. The surrounding water molecules have not been shown [9]... 

In a second example, biotinylated MCM-41 was incorporated into lipid bilayer membranes. Ion transport through the membrane was controlled by the binding of avidin. Since the assembly of the MCM particles in the membrane is random, maximum blockage rates of 80% could only be achieved. As a clear conttast, addition of bovine serum... 

In Chapter 14, Smith utilizes boronic acid carriers for the separation of hydrophilic sugars from aqueous solutions in bulk and supported liquid membrane systems. Boronic acids also function as carriers for the transport of sugars through lipid bilayers. 

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