Synthesis of cationic plastoquinone derivatives (SkQs) containing positively charged phosphonium or rhodamine moieties connected to plastoquinone by decane or pentane linkers is described. It is shown that SkQs (i) easily penetrate through planar, mitochondrial, and outer cell membranes, (ii) at low (nanomolar) concentrations, posses strong antioxidant activity in aqueous solution, BLM, lipid micelles, liposomes, isolated mitochondria, and cells, (iii) at higher (micromolar) concentrations, show pronounced prooxidant activity, the "window" between anti- and prooxidant concentrations being very much larger than for MitoQ, a cationic ubiquinone derivative showing very much lower antioxidant activity and higher prooxidant activity, (iv) are reduced by the respiratory chain to SkQH2, the rate of oxidation of SkQH2 being lower than the rate of SkQ reduction, and (v) prevent oxidation of mitochondrial cardiolipin by OH*. In HeLa cells and human fibroblasts, SkQs operate as powerful inhibitors of the ROS-induced apoptosis and necrosis. For the two most active SkQs, namely SkQ1 and SkQR1, C(1/2) values for inhibition of the H2O2-induced apoptosis in fibroblasts appear to be as low as 1x10(-11) and 8x10(-13) M, respectively. SkQR1, a fluorescent representative of the SkQ family, specifically stains a single type of organelles in the living cell, i.e. energized mitochondria. Such specificity is explained by the fact that it is the mitochondrial matrix that is the only negatively-charged compartment inside the cell. Assuming that the Deltapsi values on the outer cell and inner mitochondrial membranes are about 60 and 180 mV, respectively, and taking into account distribution coefficient of SkQ1 between lipid and water (about 13,000 : 1), the SkQ1 concentration in the inner leaflet of the inner mitochondrial membrane should be 1.3x10(8) times higher than in the extracellular space. This explains the very high efficiency of such compounds in experiments on cell cultures. It is concluded that SkQs are rechargeable, mitochondria-targeted antioxidants of very high efficiency and specificity. Therefore, they might be used to effectively prevent ROS-induced oxidation of lipids and proteins in the inner mitochondrial membrane in vivo.

No abstract

A moderately salt-tolerant and obligately alkaliphilic, chemolithoautotrophic sulfur-oxidizing bacterium, strain HL-EbGr7 T , was isolated from a full-scale bioreactor removing H 2 S from biogas under oxygen-limited conditions. Another strain, ALJ17, closely related to HL-EbGr7 T , was isolated from a Kenyan soda lake. Cells of the isolates were relatively long, slender rods, motile by a polar flagellum. Although both strains were obligately aerobic, micro-oxic conditions were preferred, especially at the beginning of growth. Chemolithoautotrophic growth was observed with sulfide and thiosulfate in a pH range of 8.0-10.5 (optimum at pH 10.0) and a salinity range of 0.2-1.5 M total Na + (optimum at 0.4 M). The genome sequence of strain HL-EbGr7 T demonstrated the presence of genes encoding the reverse Dsr pathway and a truncated Sox pathway for sulfur oxidation and enzymes of the Calvin-Benson cycle of autotrophic CO 2 assimilation with ribulose-bisphosphate carboxylase/oxygenase (RuBisCO) type I. The dominant cellular fatty acids were C 18 : 1 v7, C 16 : 0 and C 19 : 0 cyclo. Based on 16S rRNA gene sequencing, the two strains belonged to a single phylotype within the genus Thioalkalivibrio in the Gammaproteobacteria. Despite being related most closely to Thioalkalivibrio denitrificans, the isolates were unable to grow by denitrification. On the basis of phenotypic and phylogenetic analysis, the novel isolates are proposed to represent a novel species, Thioalkalivibrio sulfidiphilus sp. nov., with the type strain HL-EbGr7 T (5NCCB 100376 T 5UNIQEM U246 T ).

SummarySome organic cations are known to be electrophoretically imported into bacterial cells and actively extruded from these cells by multidrug resistance (MDR) pumps. We have studied penetration of plant antimicrobial agents berberine and palmatine and synthetic antiseptic benzalkonium chloride through black planar phospholipid membrane (BLM) and membrane of Staphylococcus aureus cells. Gradients of these cations across BLM generated an electric potential difference. Penetrating anion tetraphenyl borate and phloretin (a plant substance decreasing membrane dipole potential) stimulated this effect. Under optimal conditions, the magnitude of the electric potential was close to theoretical, that is, 60 mV/10-fold cation gradient. Berberine accumulated in S. aureus cells as shown by direct measurement of berberine with a berberinesensitive electrode. The berberine accumulation was prevented by protonophore CCCP and was stimulated by mutation in the MDR pump NorA. It is concluded that the plant alkaloids and benzalkonium are penetrating cations and substrates of an MDR pump. IUBMB Life, 52: 321 -324, 2001

No abstract