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Mitochondrial respiration is considered to provide reactive oxygen species (ROS) as byproduct of regular electron transfer. Objections were raised since results ob­tained with isolated mitochondria are commonly transferred to activities of mito­chondria in the living cell. High electrogenic membrane potential was reported to trigger formation of mitochondrial ROS involving complex I and III. Suggested bioenergetic parameters, starting ROS formation, widely change with the isolation mode. ROS detection systems generally applied may be misleading due to possible interactions with membrane constituents or electron carriers. Avoiding these prob­lems no conditions reported to transform mitochondrial respiration to a radical source were confirmed. However, changing the physical membrane state affected the highly susceptible interaction of the ubiquinol/&C1 redox complex such that ROS for­mation became possible.
The effect of some biologically active amphilic quaternary ammonium chlorides (QA) on properties of bimolecular planar membranes (BLM) formed of lipids extracted from bovine erythrocytes was studied. Ammonium salts differed in the alkyl chain length or in the non-methylene group incorporated between the hydrocarbon chain and the polar head of a molecule. It was found that in the case of a series of QA of general structure (CH3)3N+CH2OCnH2n+1 (n=4, 10, 12, 14, 16 and 18) there exists a maximal interaction between QA and BLM for QA with n=16. It was also found that the introduction of different functional groups, between the nitrogen atom and the alkyl chain of the molecule significantly changed the interaction between ammonium salts and lipid membranes. The observed changes are explained in terms of changed amphiphilic properties of the molecule.
The interaction of diphenyltin and triphenyltin chlorides with phospholipid bilayers was studied by means of 1H-NMR and differential scanning calorimetry. It is observed that diphenyltin chloride affects the phase transition of DPPC much more than triphenyltin chloride. The aromatic protons of both di- and triphenyltin chlorides give two 1H-NMR signals, which are shifted in the presence of lecithin.
Annexins belong to a family of Ca2+- and phospholipid-binding proteins that can mediate the aggregation of granules and vesicles in the presence of Ca2+. We have studied the effects of different divalent metal ions on annexin-mediated aggregation of liposomes using annexins isolated from rabbit liver and large unilamellar vesicles prepared from soybean asolectin II-S. In the course of these studies, we have found that annexin-mediated aggregation of liposomes can be driven by various earth and transition metal ions other than Ca2+. The ability of metal ions to induce annexin-mediated aggregation decreases in the order: Cd2+>Ba2+, Sr2+> Ca2+>>Mn2+>Ni2+>>Co2+. Annexin-mediated aggregation of vesicles is more selective to metal ions than the binding of annexins to membranes. We speculate that not every type of divalent metal ion can induce conformational change sufficient to promote the interaction of annexins either with two opposing membranes or with opposing protein molecules. Relative concentration ratios of metal ions in the intimate environment may be crucial for the functioning of annexins within specialized tissues and after treatment with toxic metal ions.
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