Electronic processes, bilayer lipid membranes

As described above, the ion transfer through a membrane is controlled practically by the complementary ion transfer reactions at two W/M interfaces when the M contained sufficient electrolytes. This idea was successfully applied to explanations of the following subjects concerning with membrane phenomena [20,21,26]. (1) Influence of ion transfer reaction at one W/M interface on that at another W/M interface under an applied membrane potential (2) Ion transfers through an M in the presence of the objective ion in Wl, M and/or W2 (3) Ion separation by electrolysis under an applied membrane potential (4) Ion transfer through a thin supported liquid membrane. The idea was also demonstrated to be very useful for the elucidation of ion or electron transport process through a bilayer lipid membrane (BLM), which is much thinner than a liquid membrane [21,26]. 

Electronic Processes and Redox Reactions in Bilayer Lipid Membranes... 

The electron in the electron transport chain is not free like in a metal wire. Therefore the electron motion in each act involves surmounting an energy barrier. As was shown in Refs. 16 and 108-110, a substantial role in this process is played by the conformations of the macromolecular components of the electron transport chain. Nevertheless, the simplest model systems of electron transport realized on bilayer lipid membranes were virtually based on the concept of a membrane as a thin liquid hydrocarbon in which a substance capable of redox transformations is dissolved, the products of this reaction being able to diffuse inside the bilayer. The electron transport from the aqueous phase containing a reducer amounts to injection of charges into the nonaqueous phase if it contains an electron acceptor ... 

Photosynthesis in photosynthetic bacteria involves light driven electron transfer across a bilayer lipid membrane which converts the light energy into chemical potential. After transmembrane charge separation, the chemical potential is in the form of reducing equivalents on the cytoplasmic side of the membrane, oxidizing equivalents on the periplasmic side and a membrane potential of perhaps 180 mV which is negative on the cytoplasmic side. From the crystal structure of the reaction center of Rb. sphaeroides (Yeates et (1988)) it is possible to construct an illustration of the supramolecular structure which accomplishes this process (Fig. 1). 

As a new type of electron relay, which is able to penetrate lipid membranes, we tested menaquinone (MQ, Fig. 7). Compounds of this type were not utilized earlier for artificial vesicle-based systems. However, these mimick the functioning of the Z-scheme of natural plant photosynthesis (see Figs 9 and 12). Indeed, the activity of MQ in the redox processes in a lipid bilayer membrane was revealed. However, the quantum yield of the transmembrane electron transfer from a CdS nanoparticle in the inner cavity to a CdS nanoparticle on the outer membrane surface with the participation of MQ appeared to be very low and did not exceed 0.2-0.4%. 

While the fluid mosaic model of membrane stmcture has stood up well to detailed scrutiny, additional features of membrane structure and function are constantly emerging. Two structures of particular current interest, located in surface membranes, are tipid rafts and caveolae. The former are dynamic areas of the exo-plasmic leaflet of the lipid bilayer enriched in cholesterol and sphingolipids they are involved in signal transduction and possibly other processes. Caveolae may derive from lipid rafts. Many if not all of them contain the protein caveolin-1, which may be involved in their formation from rafts. Caveolae are observable by electron microscopy as flask-shaped indentations of the cell membrane. Proteins detected in caveolae include various components of the signal-transduction system (eg, the insutin receptor and some G proteins), the folate receptor, and endothetial nitric oxide synthase (eNOS). Caveolae and lipid rafts are active areas of research, and ideas concerning them and their possible roles in various diseases are rapidly evolving. 

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