monensin and cobaltous-chloride

The complexation of carboxylic acid Monensin A (MonH, 1a) with CoCl2.6H2O and MnCl2.4H2O leads to the formation of mononuclear complexes [Co(Mon)2(H2O)2], 2a and [Mn(Mon)2(H2O)2], 2b, respectively. The unique crystal structures of 2a and 2b were determined by X-ray crystallography. The complexes crystallize in the monoclinic space group P2 1 with an octahedrally coordinated transition metal center forming the crystallographically centrosymmetric chromophore CoO6 or MnO6, respectively. Two molecules of Monensin A act bidentately through their carboxylate moiety and a hydroxyl group, and two water molecules are additionally trans-coordinated. Although the transition metal ions are not bound into the cavity of the ligand, the unusual bidentate coordination mode of the ionophore induces its "pseudo-cyclization" forming 22-membered cycles further stabilized by a number of H-bonds. The complexes are the first example of divalent metal complexes of the monovalent polyether ionophore. The parallel study on the complexation ability of the potassium complex of Monensin A (MonK, 1b) towards Co(II) and Mn(II) showed the formation of the isostructural complexes 2a and 2b accompanied by loss of the potassium ion due to the new coordination mode of the ligand. The biological tests performed with the antibiotic MonH and the corresponding metal(II) complexes show greatly enhanced antimicrobial activity of complexes 2a-b against Gram(+)-bacteria.

Topics: Anti-Bacterial Agents; Chlorides; Cobalt; Crystallography, X-Ray; Gram-Positive Bacteria; Hydrogen Bonding; Ionophores; Manganese Compounds; Microbial Sensitivity Tests; Models, Molecular; Molecular Structure; Monensin; Spectrum Analysis; Water

1. Stimulus-secretion coupling studies were carried out on adrenal chromaffin tissue from the toad. Catecholamine (CA) secretion was generated in response to acetylcholine (ACh) or high K+. 2. The response to ACh was found to be dependent on the presence of external Ca2+. The secretion induced by ACh or high K+ was inhibited by the Ca-channel blockers CoCl2 and nifedipine. 3. The specific Na+/H+ ionophore, monensin, induced a strong secretory response only if Na+ was present in the Ringer. Monensin's effect did not depend on external Ca2+ and was unaffected by the channel blockers tetrodotoxin or CoCl2. 4. Secretion induced by monensin was exocytotic as was shown by measuring ATP release using a photoluminescence, luciferine/luciferase assay. 5. In conclusion, in the toad, as in higher species, stimulus-secretion coupling involves Ca2+ entry from the external medium, possibly through voltage-dependent channels. Monensin is a potent secretagogue and the mechanism by which the ensuing elevation of intracellular Na+ concentration might induce a secretory response remains to be determined.

Topics: Acetylcholine; Adenosine Triphosphate; Adrenal Glands; Animals; Anura; Calcium; Catecholamines; Chromaffin System; Cobalt; Monensin; Nifedipine; Potassium; Sodium; Tetrodotoxin

We have subverted a receptor-mediated endocytosis event to transport genes into human leukemic cells. By coupling the natural iron-delivery protein transferrin to the DNA-binding polycations polylysine or protamine, we have created protein conjugates that bind nucleic acids and carry them into the cell during the normal transferrin cycle [Wagner, E., Zenke, M., Cotten, M., Beug, H. & Birnstiel, M. L. (1990) Proc. Natl. Acad. Sci. USA 87, 3410-3414]. We demonstrate here that this procedure is useful for a human leukemic cell line. We enhanced the rate of gene delivery by (i) increasing the transferrin receptor density through treatment of the cells with the cell-permeable iron chelator desferrioxamine, (ii) interfering with the synthesis of heme with succinyl acetone treatment, or (iii) stimulating the degradation of heme with cobalt chloride treatment. Consistent with gene delivery as an endocytosis event, we show that the subsequent expression in K-562 cells of a gene included in the transported DNA depends upon the cellular presence of the lysosomotropic agent chloroquine. By contrast, monensin blocks "transferrinfection," as does incubation of the cells at 18 degrees C.

Topics: Chloroquine; Cobalt; Deferoxamine; Heptanoates; Humans; In Vitro Techniques; Luciferases; Monensin; Phagocytosis; Polylysine; Porphobilinogen Synthase; Receptors, Transferrin; Transferrin; Transformation, Genetic; Tumor Cells, Cultured