antimycin and 2-aminoisobutyric-acid

The uptake of 3,5,3'-triiodothyronine (T3) and thyroxine (T4) was studied in human glioma cells (Hs 683) and compared with that in several other neural cell lines. At 25 degrees C or 37 degrees C, total cell uptake rose rapidly and reached equilibrium within 60 min. The glioma cells had the highest uptake: 47.6 fmol of L-T3 and 43.4 fmol of L-T4 per 10(6) cells at 37 degrees C. These were inhibited 77% and 72%, respectively, by excess unlabeled hormone. Uptake in the nuclei reached equilibrium between 90 and 120 min and was also highest in glioma cells: 1.46 fmol of L-T3 and 0.49 fmol of L-T4 per 10(6) cells. When expressed as percent of total cell uptake, however, glioma cells had the lowest values (3.1% for L-T3 and 1.1% for L-T4). Also in contrast to other cell lines, glioma cells transported L-T4 almost as effectively as L-T3. D-T3 and D-T4 total cell uptake was 86% and 96% lower than that of the respective L-isomers, and the nuclear uptake as a fraction of the cell uptake was similar. Kinetic analysis of the initial rate of cell uptake gave Vmax values for D-T3 and D-T4 that were 97% and 98% lower than for the L-isomers. Antimycin and monodansylcadaverine decreased the Vmax as well as the equilibrium cell and nuclear uptake of the L-isomers. The apparent nuclear affinity constant for L-T4 in intact cells was inhibited 90% in the presence of antimycin, whereas no effect was observed in isolated nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Aminoisobutyric Acids; Antimycin A; Binding, Competitive; Biological Transport; Cadaverine; Cell Membrane; Cell Nucleus; Glioma; Humans; Kinetics; Medulloblastoma; Neuroblastoma; Ouabain; Temperature; Thyroxine; Triiodothyronine; Tumor Cells, Cultured

Thyroid hormones must cross the plasma membrane to interact with nuclear or other intracellular receptors. In brain cells, most of the T3 in the nucleus is derived intracellularly from T4. While a saturable transport system has been demonstrated for T3 in a number of cell types, the evidence for such a system for T4 is less well established. In a mouse neuroblastoma cell line (NB41A3) the transport of T4 was found to be stereospecific, saturable, and energy dependent. When cells were incubated with radiolabeled hormone, the nuclear accumulation of L-T4 was 3.8-fold higher than that of D-T4, whereas isolated nuclei had a similar Ka for both enantiomers. Exposure of cells to antimycin and monodansylcadaverine decreased nuclear uptake of L-T4 (Ki of 197 and 55 microM, respectively), but had little effect on D-T4 uptake. Furthermore, L-system neutral amino acids, in particular L-phenylalanine at physiological concentrations, were shown to be competitive inhibitors of both T3 and T4 transport. In the presence of 0.1 mM L-phenylalanine the Km of the saturable plasma membrane transport of L-T3 increased 2.3-fold, and that of L-T4 increased 2.1-fold. In contrast, 1.0 mM L-serine or D-phenylalanine had little effect on L-T4 transport. This interaction of L-system amino acid and thyroid hormone transport may be of physiological importance.

Topics: Amino Acids; Aminoisobutyric Acids; Animals; Antimycin A; Binding, Competitive; Biological Transport, Active; Cadaverine; Cell Nucleus; Cycloleucine; Kinetics; Mice; Neuroblastoma; Phenylalanine; Stereoisomerism; Thyroxine; Triiodothyronine; Tumor Cells, Cultured

Mouse ascites-tumour cells oxidizing lactate, in a modified Ringer solution, concentrated 2-aminoisobutyrate, L-methionine or 2-(methylamino)isobutyrate about 20-fold from a 0.4 mM solution in the presence of 2-3 micrograms of nigericin/mg cellular dry wt. The ionophore increased cellular [Na+] to almost 100 mM when extracellular [Na+] was about 45 mM. Either valinomycin or the two mitochondrial inhibitors oligomycin and antimycin acting together each markedly lowered the extent to which the tumour cells concentrated amino acid, from the above factor of about 20 to roughly 2-fold. Ouabain (1 mM) had a similar effect, and further raised cellular [Na+]. The sodium pump appeared to be closely involved in amino acid uptake under these conditions.

Topics: Amino Acids; Aminoisobutyric Acids; Animals; Anti-Bacterial Agents; Antimycin A; Carcinoma, Ehrlich Tumor; In Vitro Techniques; Mice; Nigericin; Oligomycins; Ouabain; Potassium; Serum Albumin; Sodium; Valinomycin

Marquis, Robert E. (University of Rochester, Rochester, N.Y.). Nature of the bactericidal action of antimycin A for Bacillus megaterium. J. Bacteriol. 89:1453-1459. 1965.-Antimycin A, a fungicidal antibiotic which specifically inhibits metabolic reduction of cytochrome c, was found to be lethal for Bacillus megaterium. However, the bactericidal action was correlated with a capacity of antimycin to hinder plasma-membrane functions other than cytochrome-mediated respiration. With conditions under which oxygen consumption was not appreciably depressed, antimycin almost completely inhibited concentrative uptake of both alpha-aminoisobutyrate and alpha-methylglucoside, and also caused death of cells. When present in amounts greater than those required for killing or for inhibition of nutrilite uptake, antimycin also induced extensive loss of inorganic phosphate and other substances from whole cells, inhibited aerobic respiration, and acted as a lytic agent for isolated protoplasts. The lytic potency of antimycin was greater, on a molar basis, than that of digitonin, hexachlorophene, polymyxin B, and all but one of a number of test detergents. Protoplasts concentrated antimycin primarily in or on the plasma membrane, and the refractive index of isolated protoplast membranes rose sharply as a result of antimycin binding. In all, antimycin-induced lysis appeared not to include dissolution of the protoplast membrane similar to that produced by dodecyl sulfate. Rather, the lytic process seemed more akin to that induced by cationic detergents or by polymyxin.

Topics: Aminoisobutyric Acids; Anti-Bacterial Agents; Antifungal Agents; Antimycin A; Bacillus megaterium; Bacteriolysis; Butyrates; Cell Membrane; Cell Membrane Permeability; Cytochromes; Glycosides; Manometry; Metabolism; Methylglucosides; Pharmacology; Phosphates; Polymyxin B; Polymyxins; Protoplasts; Research; Spectrophotometry; Surface-Active Agents