Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cations”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69Linked to original sources
PubMed2002

Role of cation-pi interactions to the stability of thermophilic proteins.

Elucidating the factors responsible for exhibiting extreme thermal stability of thermophilic proteins is very important for an understanding of the mechanism of protein stability, as well as to design stable proteins. In this work, we have analyzed the influence of cation-pi interactions to enhance the stability from mesophilic to thermophilic proteins. The favorable residue pairs forming such a system of interactions have been brought out. We found that the Tyr has a greater number of such interactions with Lys in thermophilic proteins. Specifically, the same Lys would experience a greater number of cation-pi interactions with several Tyr residues in thermophiles. On the other hand, the influence of Phe in making cation-pi interactions is higher in mesophiles than in thermophiles. Further, a network of cation-pi interactions are maintained by Lys in thermophiles, whereas Arg plays a major role in mesophilic proteins. Moreover, atoms that have a substantial positive charge in both Lys and Arg make a more significant contribution for cation-pi interactions than do cationic group atoms.

Amino Acids, Aromatic↗
PubMed1979

Localization of submembranous cations to the leading end of human neutrophils during chemotaxis.

Potassium pyroantimonate was used to localize sites of bound cations in human neutrophils under conditions of random migration, stimulated random migration (chemokinesis), and directed migration (chemotaxis). The cells were placed in a standard chamber in which 0.45-micron micropore filters separated the cells from the stimulus (buffer, Escherichia coli endotoxin-activated serum or the synthetic chemotactic peptide N-formyl-Met-Leu-Phe). The small pore filters permitted pseudopod formation but impeded cell imgration through the filter. Cells examined under all conditions had electron-dense precipitates of antimonate salts in some granules. However, antimonate deposits were localized in the condensed chromatin of the nucleus during random migration and associated to a large extent with the uncondensed nuclear chromatin during chemokinesis and chemotaxis. Under conditions of chemokinesis deposition of antimonate procipitates appeared on the cytoplasmic side of the plasma membrane of neutrophils whereas under conditions of chemotaxis cation deposits beneath the cell membrane were localized to the pseudopods which were directed toward the chemoattractant. In addition to endotoxin-activated serum, concentrations of N-formyl-Met-Leu-Phe which caused neutrophil chemotaxis (10(-8) M) also caused cation deposition beneath the cell membrane at the leading end of the cell regardless of whether albumin was present in the incubation media. However, with higher concentrations of the synthetic peptide (10(-5) M) which caused granule release and were not chemotactic, submembranous cation deposition was not seen. EDTA (10 mM) and EGTA (10 mM) removed nuclear, granular, and submembranous cation deposits from neutrophils examined under conditions of chemotaxis. X-ray microprobe analysis of antimonate deposits revealed the possible presence of calcium but did not detect sodium or magnesium. The data indicate that chemotactic factors induce submembranous deposition of cations, most likely Ca++, which localize to the leading edge of cells exposed to a gradient of chemoattractant.

Antimony↗
PubMed1961

The effects of mammalian and other cationic polypeptides on the cytochemical character of bacterial cells.

Cationic polypeptides interact with bacterial cells of E. coli and B. anthracis. They confer upon the cells some of the characteristics of cationic particles. Since bacterial cells usually behave as anions, acidic dyes at high pH levels differentiate between cells which have and those which have not interacted with cationic polypeptides. Under the conditions of these experiments it appeared that cationic polypeptides tend to be sorbed in highest concentration in the surface layers of the cells. Electrovalent binding to anionic cell components and detergent action are probably among the mechanisms involved in the interaction between the polypeptides such as histones and bacterial cells. The differential staining of bacterial cells which have interacted with cationic polypeptides is feasible and reasonably selective. It should be useful in determining whether bacterial cells interact with host cationic polypeptides in vitro.

Animals↗
PubMed1965

Mediators of inflammation in leukocyte lysosomes. II. Mechanism of action of lysosomal cationic protein upon vascular permeability in the rat.

The vascular permeability-increasing action of rabbit PMNL lysosomes has been studied in skin and cremaster muscle of the rat. Both an extract of frozen-thawed granules and a cathepsin-free cationic protein fraction of the granules (which had previously been demonstrated to cause leukocyte adhesion and emigration in vivo) induce increased vascular permeability in skin and muscle which resembles that produced by histamine or histamine-liberators with respect to the timing of the response and the predominant type of microvessel affected. Extracts of frozen-thawed lysosomes and the inflammatory lysosomal cationic protein both cause disruption of rat mesenteric mast cells in vitro, whereas a granule-free cytoplasmic fraction of PMN leukocytes and a non-inflammatory cationic protein fraction of the granules do not do so under identical test conditions. The mastocytolytic action of lysosomal materials in vitro is not inhibited in the presence of 10 kallikrein-inhibiting units of trasylol per ml. The mast cell rupturing fraction of PMNL granules (cationic protein) possesses no detectable peroxidase activity or acid-mucopolysaccharase activity. When compared with compound 48/80 on the basis of estimated molecular weight, the lysosomal cationic protein appears to be at least as active as the latter compound with respect to in vitro mastocytolytic potency. Chronic pretreatment of rats with an agent known to reduce tissue mast cell numbers causes marked suppression of the vascular permeability change normally induced in skin and muscle by lysosomal extracts and cationic protein. Similar results are obtained if lysosomal materials are tested in rats pretreated with an antihistaminic. These observations are discussed with respect to the mode of action of PMNL lysosomes in the early and late phases of local tissue-injury reactions.

Animals↗
PubMed2005

Functional role and affinity of inorganic cations in stabilizing the tetrameric structure of the KcsA K+ channel.

Crystal structures of the tetrameric KcsA K+ channel reveal seven distinct binding sites for K+ ions within the central pore formed at the fourfold rotational symmetry axis. Coordination of an individual K+ ion by eight protein oxygen atoms within the selectivity filter suggests that ion-subunit bridging by cation-oxygen interactions contributes to structural stability of the tetramer. To test this hypothesis, we examined the effect of inorganic cations on the temperature dependence of the KcsA tetramer as monitored by SDS-PAGE. Inorganic cations known to permeate or strongly block K+ channels (K+, Rb+, Cs+, Tl+, NH4+, Ba2+, and Sr2+) confer tetramer stability at higher temperatures (T0.5 range = 87 degrees C to >99 degrees C) than impermeant cations and weak blockers (Li+, Na+, Tris+, choline+; T0.5 range = 59 degrees C to 77 degrees C). Titration of K+, Ba2+, and other stabilizing cations protects against rapid loss of KcsA tetramer observed in 100 mM choline Cl at 90 degrees C. Tetramer protection titrations of K+, Rb+, Cs+, Tl+, and NH4+ at 85 degrees C or 90 degrees C exhibit apparent Hill coefficients (N) ranging from 1.7 to 3.3 and affinity constants (K0.5) ranging from 1.1 to 9.6 mM. Ba2+ and Sr2+ titrations exhibit apparent one-site behavior (N congruent with 1) with K0.5 values of 210 nM and 11 microM, respectively. At 95 degrees C in the presence of 5 mM K+, titration of Li+ or Na+ destabilizes the tetramer with K0.5 values of 57 mM and 109 mM, respectively. We conclude that specific binding interactions of inorganic cations with the selectivity filter are an important determinant of tetramer stability of KscA.

Bacterial Proteins↗
PubMed1998

Aerosolization of cationic lipid:pDNA complexes--in vitro optimization of nebulizer parameters for human clinical studies.

Previously, we have described the optimization of the aerosol delivery of a nonviral gene therapy vector to the lungs of rodents (Eastman et al., 1997b). Although aerosolizing cationic lipid:pDNA complexes into a whole-body exposure chamber resulted in high levels of reporter gene expression in the lungs of BALB/c mice, the conditions employed were not optimal for the delivery of lipid:pDNA complexes to the lungs of human patients. That is, the consumption rate of the material in the nebulizer, and thus the delivery time, were very slow and the aerosol was delivered in a continuous flow. Here we describe in vitro experiments used to develop a cationic lipid:pDNA aerosol with characteristics more suitable for delivery to the lungs of humans, as a necessary prerequisite for conducting a clinical study with human cystic fibrosis patients. Using cascade impactors and all-glass impingers, we have screened several commercially available nebulizers for their ability to deliver intact, respirable, active lipid:pDNA complexes in the shortest time possible, and have identified the Pari LC Jet Plus nebulizer as the optimal nebulizer that meets these criteria. Using this nebulizer in an intermittent mode to mimic breath actuation, consumption rates of approximately 0.6 ml/min of the cationic lipid:pDNA complexes (6 mM cationic lipid:8 mM pDNA) were obtained. The plasmid DNA remained intact and the complexes were shown to maintain activity throughout the nebulization run. Based on measurements of the nebulized dose and the mass median aerodynamic diameter, we calculate a delivered dose of approximately 22 micromol (7.2 mg) of pDNA for each 8 ml of cationic lipid:pDNA complex aerosolized to the lungs of a human patient. This dose should be sufficient to test the clinical efficacy of cationic lipid-mediated gene delivery for the treatment of cystic fibrosis.

Aerosols↗
PubMed2006

Multiple pathways for cationic amino acid transport in rat seminiferous tubule cells.

Arginine and ornithine are known to be important for various biological processes in the testis, but the delivery of extracellular cationic amino acids to the seminiferous tubule cells remains poorly understood. We investigated the activity and expression of cationic amino acid transporters in isolated rat Sertoli cells, peritubular cells, pachytene spermatocytes, and early spermatids. We assessed the l-arginine uptake kinetics, Na(+) dependence of transport, profiles of cis inhibition of uptake by cationic and neutral amino acids, and sensitivity to trans stimulation of cationic amino acid transporters, and studied the expression of the genes encoding them by RT-PCR. Our data suggest that l-arginine is taken up by Sertoli cells and peritubular cells, principally via system y(+)L (SLC3A2/SLC7A6) and system y(+) (SLC7A1 and SLC7A2), with system B(0+) making a minor contribution. By contrast, system B(0+), associated with system y(+)L (SLC3A2/SLC7A7 and SLC7A6), made a major contribution to the transport of cationic amino acids in pachytene spermatocytes and early spermatids. Sertoli cells had higher rates of l-arginine transport than the other seminiferous tubule cells. This high efficiency of arginine transport in Sertoli cells and the properties of the y(+)L system predominating in these cells strongly suggest that Sertoli cells play a key role in supplying germ cells with l-arginine and other cationic amino acids. Furthermore, whereas cytokines induce nitric oxide (NO) production in peritubular and Sertoli cells, little or no upregulation of arginine transport by cytokines was observed in these cells. Thus, NO synthesis does not depend on the stimulation of arginine transport in these somatic tubular cells.

Amino Acid Transport Systems, Basic↗
PubMed1997

Nitric oxide and effects of cationic polypeptides in canine cerebral arteries.

Cationic polypeptides are released by activated leukocytes and may play an important role in the regulation of vascular tone. Effects of cationic polypeptides on cerebral vascular tone have not been studied. The present experiments were designed to determine if synthetic cationic polypeptides, poly-L-arginine and poly-L-lysine, affect the function of cerebral arteries. Rings of canine basilar arteries with and without endothelium were suspended for isometric force recording. Poly-L-arginine (10(-8)-10(-7) M) and poly-L-lysine (10(-8)-10(-7).M) caused endothelium-dependent relaxations. A nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (10(-4) M), and a nitric oxide scavenger, oxyhemoglobin (3 x 10(-6) M), inhibited relaxations in response to cationic polypeptides. Negatively charged molecules, heparin (1 U/ml) and dextran sulfate (10 mg/ml), also inhibited relaxations to poly-L-arginine or poly-L-lysine. Higher concentrations of poly-L-arginine (10(-6)-10(-5) M) and poly-L-lysine (10(-6)-10(-5) M) induced endothelium-independent contractions. A protein kinase C inhibitor, staurosporine (10(-8) M), abolished these contractions. Heparin (10 U/ml) and dextran sulfate (100 mg/ml) inhibited the contractile effect of cationic polypeptides but did not affect contractions to phorbol 12,13-dibutyrate. Poly-L-arginine (10(-6) M) and poly-L-lysine (10(-6) M) abolished endothelium-dependent relaxations in response to bradykinin (10(-10)-10(-6) M) or calcium ionophore A23187 (10(-9)-10(-6) M). Heparin (50 U/ml) and dextran sulfate (200 mg/ml) restored endothelium-dependent relaxations to bradykinin (10(-10)-10(-6) M) in arteries exposed to poly-L-arginine (10(-6) M) or poly-L-lysine (10(-6) M). These studies demonstrate that in the lower concentration range (10(-8)-10(-7) M), poly-L-arginine and poly-L-lysine induce endothelium-dependent relaxations by production of nitric oxide via charge-dependent activation of endothelial nitric oxide synthase. In the higher concentration range (10(-6)-10(-5) M), cationic polypeptides cause endothelium-independent contractions as well as impairment of endothelium-dependent relaxations in response to bradykinin and A23187. These contractions and inhibition of endothelium-dependent relaxations are also mediated by a charge-dependent mechanism and may involve activation of protein kinase C.

Animals↗
PubMed1978

Cytoplasmic vacuoles of Rous virus transformed cells are organelles involved in cation uptake.

Cytoplasmic vacuoles induced during transformation of cells by Bryan strain Rous sarcoma virus (RSV-BH) have been studied using the cationic dye, neutral red(NR). Both the rate of uptake and the accumulation of NR are greater in RSV-BH transformed cells than non-transformed cells however, uptake was greater in vacuolated than in non-vacuolated cells, whether or not they were transformed. The NR was incorporated into pre-existing vacuoles in the absence of cytoplasmic staining, suggesting the existence of direct channels from the cell surface to the vacuoles. Other low mol. wt. cationic dyes could also be incorporated into vacuoles, although those with branched structures or cationic weights greater than 330 were excluded. No anionic dyes were incorporated. Infection of cells with a virus mutant, RSV-BH-Ta, induces temperature-dependent vacuolization. After a shift to the vacuole-permissive temperature, vacuoles developed at different rates and with morphological variations with different cations. Vacuoles which had formed in the presence of several cations, (K+, Rb+, tris+, choline+) failed to disappear when cells were incubated at a temperature sufficient to revert vacuoles formed in Na+-containing medium. No short-term effects of Cl-replacements (Br-, I-, or SO2-4) on vacuolization or reversal were observed. The results suggest that these vacuoles are organelles involved in cation uptake. A possible function for these organelles in RSV-BH induced malignancy is discussed.

Animals↗
PubMed1993

Effect of Cations on Effective Permeability of Leaf Cuticles to Sulfuric Acid.

Many plants are exposed to prolonged episodes of anthropogenic acid precipitation with pH values of 4 or less, but there is little evidence of widespread direct damage to the plant cells. Acids appear to permeate leaf cuticle via charged pores, which act as a fixed buffer that delays but does not stop acid movement. We investigated the effect of cations on the movement of protons through astomatous isolated leaf cuticles of pear (Pyrus communis L.) and rough lemon (Citrus limon [L.] Burm. fils cv Ponderosa). Chloride salt solutions of Na, K, Ca, Cd, Mg, Gd, or Y in a diffusion apparatus were applied to the morphological inner surface of the cuticle, while the outer surface faced a large volume of pH 3 or 4 sulfuric acid. Effective permeability was calculated from the change in the pH of the inner solution as measured with a pH microelectrode. Monovalent cations caused either no change (pear) or promotion (rough lemon) of proton movement. Divalent cations reduced proton movement in a concentration-dependent manner (both species), whereas trivalent cations (rough lemon only) caused the effective permeability to decrease to near zero. Inhibition by 10 mM CaCl2 was reversed with water. The effects of these cations on the permeability of cuticles to protons was used to elucidate mechanisms by which cations can protect leaves from acid precipitation in nature.

Journal Article↗
PubMed1969

Effect of adsorbed cations on phosphorus uptake by excised roots.

Pretreatment of excised roots of Hordeum vulgare, Zea mays, and Glycine max with various salt solutions affected their subsequent rate of phosphorus absorption from 2 x 10(-5)m KH(2)PO(4). The rate of absorption was greatest for roots pretreated with trivalent cations, intermediate with divalent cations and lowest with monovalent cations. It appeared that the pretreatment involved a rapid exchange reaction at the root surface which was reversible. A 1 min pretreatment was effective for more than 20 min. The acceleration of phosphorus uptake by roots produced by polyvalent cations may be due partly or entirely to a greater reduction in the electrical potential at the root surface or within the pores of the negatively charged cell wall by polyvalent cations than by monovalent cations.

Journal Article↗
PubMed2005

Structure of gramicidin D-RbCl complex at atomic resolution from low-temperature synchrotron data: interactions of double-stranded gramicidin channel contents and cations with channel wall.

Gramicidin D (gD) is a naturally occurring ionophoric antibiotic that forms membrane channels specific for monovalent cations. The crystal structure of the RbCl complex of gD has been determined at 1.14 A resolution from low-temperature (100 K) synchrotron-radiation data with a final R of 16%. The structure was refined with anisotropic temperature factors for all non-H atoms and with partial occupancies for many of them. The asymmetric unit in the crystal contains four crystallographically independent molecules that form two right-handed antiparallel double-stranded dimers. There are seven distinct rubidium-binding sites in each dimeric channel. The occupancy factors of Rb cations are between 0.11 and 0.35 and the total ion contents of the two crystallographically independent channels are 1.59 and 1.22 ions, respectively. Although each channel is 'chemically symmetrical', the side-chain conformations, the distributions of rubidium cations and their binding sites in the two independent channels are not. Cations are 'coordinated' by delocalized pi-electrons of three to five carbonyl groups that together with peptide backbone chains form the gramicidin channel walls. The water:cation ratio in the channel interior is four or five:one, and five or six waters separate Rb cations during their passage through the channel.

Binding Sites↗
PubMed1985

Cutaneous deposition of immune complexes in chronic serum sickness of mice induced with cationized or unaltered antigen.

We have previously shown that cationic proteins localize to the dermal-epidermal junction (DEJ) after i.v. injection in experimental animals. In the present studies, cationized rabbit IgG was used as antigen for induction of chronic serum sickness in C57BL/6J mice over a period of 4 weeks. The formation of immune deposits was examined by immunofluorescence microscopy at weekly intervals during chronic antigen administration and at 7 weeks from the initiation of studies. Chronic administration of the cationized antigen led to immune complex deposits at the DEJ, while administration of the same antigen in native form did not lead to these deposits. Junctional immune deposits increased with higher doses of cationized antigen and paralleled renal extraglomular deposition in intensity, persistence, and morphology. Mice given cationized antigen also demonstrated vascular immune complex deposits without complement, while mice given native antigen had complement deposits and developed perivascular inflammation. No inflammation or complement deposition was detected at the DEJ in either group. Charge properties of circulating antigens are important in determining tissue sites of immune complex deposition and inflammation. Circulating cationic antigens can lead to immune deposits at the DEJ.

Animals↗
PubMed1997

ATPase gene transfer and mutational analysis of the cation translocation mechanism.

The peptide segment interposed between cation binding and phosphorylation domains retains a high degree of homology in all cation transport ATPases. Mutational analysis and chimeric replacements of Ca2+ ATPase components with corresponding Na+,K(+)-ATPase components indicate that this segment is utilized by various cation ATPases as a common structural device for a long-range functional linkage of enzyme phosphorylation and cation transport. Vectorial displacement of bound cation is rendered possible by a transmembrane channel formed by four clustered helices (M4, M5, M6, and M8). Originating from the four helices, the oxygen functions of Glu309, Glu771, Thr799, Asp800, and Glu908 form a duplex Ca2+ binding site in the middle of the channel, while Lys297 seals the luminal end of the channel with its positively charged side chain. The perturbation triggered by enzyme phosphorylation is apparently transmitted through the linkage segment to produce rotational displacement of the M4 helix with minimal change of secondary structure. The cation binding site is thereby disrupted and the Lys297 side chain removed, permitting Ca2+ to dissociate in exchange for H+ and to flow through the luminal end of the channel.

Amino Acid Sequence↗
PubMed1972

Extracellular cations and the movement of choline across the erythrocyte membrane.

1. The ability of human erythrocytes to accumulate choline is abolished when external Na is replaced by Cs, Rb, K or Li but is increased when the external cation is Mg or Ca.2. The unidirectional influx of choline is reduced when external Na is replaced by other monovalent cations but is not changed when Na is replaced by Mg or Ca.3. The unidirectional efflux of choline into a choline-free medium is increased when external Na is replaced by other monovalent cations and markedly reduced when Na is replaced by Mg or Ca. When the external medium contains 1 mM choline, changing the external cation has virtually no effect on the rate of choline efflux.4. When the extracellular concentrations of K and Na are similar to that found in the intracellular water, choline appears to become passively distributed across the cell membrane; when the extracellular K is then replaced by Cs a net efflux of choline against a concentration gradient results.5. It is concluded that the choline carrier may be described as a cation carrier with a high affinity for choline and affinities for Cs > Rb > K > Li > Na and that these monovalent cations can cross the membrane on the choline transport system.

Biological Transport, Active↗
PubMed1969

Cation-binding capacity of membranes isolated from Micrococcus lysodeikticus.

A study was made of H(+), Na(+), K(+), Ca(++), and Mg(++) binding and ion-exchange properties of the plasma-mesosome membrane system isolated from Micrococcus lysodeikticus strain NCTC 2665. Titration curves were obtained on membranes prepared according to the method of M. R. J. Salton and further exposed to pH 4 for 4 hr (membranes-H). The dissociation coefficients and binding capacities were obtained by applying the mass law equation and the plot of G. Schatchard to the data. The membranes-H possess four kinds of dissociable groups with pK 4.96, 4.18, 3.60, and 3.09, respectively, and a total binding capacity of 0.65 meq/g (dry weight). Potentiometric titrations of cations in the presence and in the absence of membranes-H show that cations (Na(+), K(+), Ca(++), and Mg(++)) are bound by the dissociated groups of the membrane. The fall in pH value for bivalent cations is greater than that for monovalent cations. Cations of the same valency produce equal diminutions on pH. Furthermore, ion-exchange tests carried out on membranes saturated with Mg(++) or Na(+) and suspended in a medium containing (45)Ca show that the cations are reversibly bound.

Calcium↗
PubMed1966

Role of Multivalent Cations in the Organization, Structure, and Assembly of the Cell Wall of Pseudomonas aeruginosa.

Asbell, Mary A. (University of Georgia, Athens), and R. G. Eagon. Role of multivalent cations in the organization, structure, and assembly of the cell wall of Pseudomonas aeruginosa. J. Bacteriol. 92:380-387. 1966. -Incubation of Pseudomonas aeruginosa with ethylenediaminetetraacetate induced the formation of osmotically fragile rods termed osmoplasts. These could be restored to osmotically stable forms by multivalent cations. Only those cells restored by divalent cations normally found in the cell wall were capable of multiplication. The respiration of restored cells, however, was unimpaired, irrespective of whether they were capable of multiplication. Moreover, the permeability characteristics of osmoplasts and restored cells were unimpaired. When multivalent cations were chelated from the cell wall and replaced by sodium, a weakened cell wall and an osmotically fragile cell resulted. This was apparently caused by the absence of cross-linkages in the cell wall via multivalent cations. Tris(hydroxymethyl)aminomethane buffer compounded the lethal effects of ethylenediaminetetraacetate. The lipopolysaccharide component was inferred to be the site of attack by ethylenediaminetetraacetate. A mechanism for the synthesis of the lipopolysaccharide sacculus was proposed whereby negatively charged subunits are "trapped" by forming ionic and coordinate bonds intermediated by multivalent cations.

Journal Article↗
PubMed1967

Gramicidin, valinomycin, and cation permeability of Streptococcus faecalis.

Gramicidin and valinomycin in concentrations of 10(-7) and 10(-6)m, respectively, inhibited the growth of Streptococcus faecalis. Inhibition of growth was associated with loss of Rb(+) and K(+) from the cells, and could be reversed by addition of excess K(+). Cells treated with these antibiotics exhibited greatly increased permeability to certain cations; no effect was observed on the penetration of other small molecules. Unlike normal cells, cells treated with gramicidin rapidly lost internal Rb(+) by passive exchange with external cations, including H(+), all monovalent alkali metals, NH(4) (+), Mg(++), and tris(hydroxymethyl)aminomethane. Exchange was rapid even at 0 C and was independent of energy metabolism. The effect of valinomycin was more selective. Cellular Rb(+) was rapidly displaced by external H(+), K(+), Rb(+), and Cs(+); other cations were less effective. The exchange was independent of metabolism but strongly affected by temperature. Under certain conditions, polyvalent cations inhibited exchange between (86)Rb and Rb(+) induced by valinomycin. The antibiotic apparently neither stimulates nor inhibits the energy-dependent K(+) pump of S. faecalis, but exerts its effect on the passive permeability of the membrane to cations. The increased permeability to specific cations induced by gramicidin and valinomycin is a sufficient explanation for the inhibition of growth, glycolysis, and other processes.

Anti-Bacterial Agents↗