Membranes architecture

Traditionally, the electron and proton transport pathways of photosynthetic membranes (33) have been represented as a "Z" rotated 90° to the left with noncycHc electron flow from left to right and PSII on the left-most and PSI on the right-most vertical in that orientation (25,34). Other orientations and more complex graphical representations have been used to depict electron transport (29) or the sequence and redox midpoint potentials of the electron carriers. As elucidation of photosynthetic membrane architecture and electron pathways has progressed, PSI has come to be placed on the left as the "Z" convention is being abandoned. Figure 1 describes the orientation in the thylakoid membrane of the components of PSI and PSII with noncycHc electron flow from right to left. 

Understanding mechanisms controlling metabolon localization in plastids of different membrane architectures Little is known about metabolon structure, assembly, and membrane targeting. The carotenoid biosynthetic pathway exists on plastid membranes. However, plastids have different membrane architectures and therefore tissue- and plastid-specific differences in membrane targeting of the biosynthetic metabolon can be expected. Localization in chloroplasts that harbor both thylakoid and envelope membranes differs from the envelope membranes in endosperm amy-loplasts. In fact, localization on both thylakoid and envelope membranes implies that the carotenoid pathway is really not a single pathway, but a duplicated pathway that may very well have membrane-specific roles with regard to functions in primary and secondary metabolism. 

Enhancement of tight junctions of cell membrane architecture. 

The only internationally used drug effective for treating schistosomiasis is praziquantel. This drug induces a rapid influx into the worms of surrounding Ca2+, a process that leads to paralysis (Martin, 1997), and changes in the surface membrane architecture that lead to the exposure of worm antigens that are normally cryptic (Brindley and Sher, 1987). Parasites affected in this way become susceptible to antibody-mediated immune attack and are killed as a result of the synergistic actions of chemotherapy and the immune response (Doenhoff et al., 1987 Brindley etal., 1989). 

Recently another electrically assisted drug delivery technology, electroporation, was proposed as an alternative or adjuvant to iontophoresis. Electroporation comprises the use of electric pulses to induce transient changes in the cell membrane architecture that turn it into more permeable barrier. Beside the permeabilization effect on cell membrane, it was postulated that this technique induces electrophoretic effect on charged macromolecules and drives them to move across the destabilized membrane [205]. 

Most important for the regulation of the membrane architecture are membrane potential, intracellular Ca2+ concentration, pH, changes in lipid composition due to the action of phospholipases and cell-cell coupling as well as the coupling of the membrane to the cytoskeleton and the extracellular matrix. Membrane architecture is additionally modulated by ions, lipo- and amphiphilic hormones, metabolites, drugs, lipid-binding peptide hormones, and amphitropic proteins [44]. 

Landh, T. (1996) Cubic Cell Membrane Architectures — Taking Another Look at Membrane Bound Cell Spaces. Thesis, Dept of Food Technology, Lund University, Lund, Sweden. 

Lipid rafts were originally proposed as an explanation for a non-random membrane architecture and their function was originally thought to be linked with membrane trafficking. However, rafts proved to be able to influence organization of membrane receptors and bioactivity as well as membrane trafficking. 

In cells, a particular composition and the physicochemical properties of the lipid matrix at given ambient conditions represent the basis for a normal functioning [3]. Any disturbance of the composition due, e. g., to different net charges or acylation patterns may result in changes of membrane fluidity/permeability, in phase separation, or in disruption of the lamellar membrane architecture. However, cells are potentially able to overcome such changes in lipid matrix composition by altering it ( homovicious adaptation ) [4]. If an adaptation of this type does not take place, severe dysfunction of a cell may occur. 

Springer EL, Hakett AJ Nelson-Rees WA (1976) Alteration of the cell membrane architecture during suspension and monolayer culturing. International Journal of Cancer 17 407-413. 

Fig. 9.2. Schematic representation of main types of pore structures and membrane architectures (A) straight cylindrical pores (B) straight as)onmetric pores (C) tortuous pore system.

In the case of supported membranes the effect of the support has always to be evaluated, and if not negligible, corrections for support effects should be applied even with simple membrane architectures. 

Permeation and separation data reported in the literature are difficult to compare directly. This is due to the variety of parameters which influence the absolute value of permeation and separation data and which are usually badly described and sometimes cannot even be adequately described. As is shown in the preceding sections the pressure conditions and the flow dynamics (aerodynamic conditions) play a very important role. These pressure conditions are not always adequately described and data describing the external flow conditions do not directly reflect flow conditions in the membrane (model design and/or membrane architecture playing a role). 

At least two obvious aspects must be considered here, namely the influence of the membrane lipids on sphingomyelinase activity, and the effects of the enzyme on the membrane properties. For the latter, we shall deal separately with enzyme effects on membrane permeability and effects on membrane architecture. 

And finally, the very promising application of hydrogels as cushions but also as protective coatings for the tethered membrane architectures, eventually allowing even for operations in air, is presented and discussed. 

Lipo-Glycopolymers as Building Blocks for Tethered Membrane Architectures. . 98... 

Plasma-Polymer Layers as Cushions for Lipid Membrane Architectures. 105... 

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