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At least 19 recordsLinked to original sources
PubMed1978

Evidence for anionic cation transport of lithium, sodium and potassium across the human erythrocyte membrane induced by divalent anions.

1. The passive net transport of Li+ and Na+ across the human red cell membrane was accelerated by the divalent anions carbonate, sulphite, oxalate, phosphite and malonate. Phthalate, maleate, sulphate and succinate were found additionally to stimulate downhill transport of K+. Marked differences in anion efficacy and selectivity were observed. 2. The effects of these 'carbonate type' anions were reversible and fully blocked by SITS, dipyridamole and other inhibitors of anion transfer. 3. Cation transport acceleration induced by the monovalent anions salicylate, benzoate, thiocyanate and 2,4-dinitrophenol were inhibited by dipyridamole, but not affected by SITS. A great number of mono- and polyvalent anions were without detectable influence on Li+ transport. 4. Li+ net uptake induced by oxalate exhibited a pH dependence similar to that reported for halide self exchange. 5. Transport acceleration by carbonate type anions displayed a linear, 1:1 dependence on the concentrations of both the anion and the cation and was symmetric with respect to the two sides of the membrane. 6. It is concluded that the divalent carbonate type anions form singly charged, negative 1:1 ion pairs with the respective alkali metal cations, the ion pairs traversing the red cell membrane via the anion exchange pathway. This concept of anionic formation of some of the ion pairs considered. The relative efficacies and cation selectivities of polyvalent anions can largely be explained on the basis of electrostatic interactions governing ion pair formation. However, the chelating properties, structural flexibility, polarizability of the anions and the accessibility of the ion pairs to the anion exchange pathway need also be considered. 7. An exchange of NaCO-3 ion pairs for internal HCO-3 or Cl- is discussed as a possible mode of cellular pH regulation.

Anions↗
PubMed1976

The interaction of an anionic photoreactive probe with the anion transport system of the human red blood cell.

N-(4-azido-2-nitrophenyl)-2-aminoethyl[35S]sulfonate is employed as a photoreactive probe for the anion transport system in the human erythrocyte. In the dark and at 37 degrees C the probe penetrates the membrane via a pathway sensitive to specific inhibitors of anion permeability. It reversibly inhibits sulfate and chloride fluxes but the inhibition is reduced by higher concentrations of sulfate. Upon photolysis to produce a reactive nitrene (at 0 degrees C to minimize penetration), the probe inhibition of anion permeability. Under appropriate conditions the degree of inhibition after photoactivation (irreversible) is almost the same as that in the dark (reversible). The binding sites for the radioactive probe are largely found in proteins of 95 000 apparent molecular weight (band 3). After pronase treatment of the labelled cells, most of the probe is found in a 65 000 molecular weight segment derived from the 95 000 molecular weight protein. In this respect the photoreactive probe resembles another potent irreversible inhibitor of anion transport, 4, 4'-diisothiocyano-2, 2' stilbene disulfonate. In fact, most of the binding sites for each probe are common to both. Thus, in the dark, the azido derivative protects the anion system from inhibition by DIDS and substantially reduces the binding of DIDS to band 3 protein. Conversely, pretreatment with DIDS substantially reduces the binding of the photoreactive probe to the same protein. The fact that an apparent substrate for the anion permeation system competes for binding sites with a specific non-penetrating inhibitor of anion permeability suggests that the inhibitory and transport sites may be closely related and implicates the 95 000 molecular weight protein as the element of the anion transport system which contains the substrate binding site.

Biological Transport↗
PubMed1979

Electrolyte secretion by the isolated cat pancreas during replacement of extracellular bicarbonate by organic anions and chloride by inorganic anions.

1. The effect of replacing extracellular bicarbonate and chloride by other anions on the volume and composition of secretin-stimulated pancreatic juice has been analysed in the isolated, perfused cat pancreas. 2. The anions of some aliphatic carboxylic acids were able partially to substitute for bicarbonate in sustaining pancreatic secretion. The order of effectiveness was: acetate greater than proprionate greater than butyrate greater than formate. 3. The rate of secretion in the presence of 25 mM-acetate was 42% of that achieved with 25 mM-bicarbonate. The concentration of acetate in the secretion varied with flow rate, reaching a maximum of 120 mM at high flow rates and declining at lower flow rates, with reciprocal changes in chloride concentration. Bicarbonate was always present in the secretion at a concentration of 5--7 mM. 4. Inorganic anions were able totally or partially to substitute for chloride in sustaining secretion. In relation to chloride, their degree of effectiveness was: chloride = bromide = or greater than nitrate greater than iodide greater than sulphate greater than methyl sulphate greater than isethionate. Those anions which had no effect on secretion rate (i.e. bromide and nitrate) also had no effect on the bicarbonate concentration of the secretion and themselves appeared in the secretion in place of chloride. Those anions which inhibited secretion increased the bicarbonate concentration in the secretion in proportion to the degree of inhibition they caused (i.e. the increase was greatest with isethionate). 5. When perfusate chloride was only partially replaced by bromide or iodide the ratios of chloride: bromide and chloride: iodide in the secretion were approximately equal to those in the perfusate. 6. The carbonic anhydrase inhibitor acetazolamide reduced secretory rate and bicarbonate concentration when added to normal perfusion fluid or chloride-substituted fluids, but had no effect following replacement of perfusate bicarbonate by acetate. 7. These observations illustrate that an extracellular source of permeant anions is required for optimal pancreatic bicarbonate secretion to occur. This may indicate the participation of an anion exchange carrier in the transport events responsible for this secretory process.

Acetazolamide↗
PubMed1977

The relationship between anion exchange and net anion flow across the human red blood cell membrane.

The conductive (net) anion permeability of human red blood cells was determined from net KCl or K2SO4 effluxes into low K+ media at high valinomycin concentrations, conditions under which the salt efflux is limited primarily by the net anion permeability. Disulfonic stilbenes, inhibitors of anion exchange, also inhibited KCl or K2SO4 efflux under these conditions, but were less effective at lower valinomycin concentrations where K+ permeability is the primary limiting factor. Various concentrations of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) had similar inhibitory effects on net and exchange sulfate fluxes, both of which were almost completely DIDS sensitive. In the case of Cl-, a high correlation was also found between inhibition of net and exchange fluxes, but in this case about 35% of the net flux was insensitive to DIDS. The net and exchange transport processes differed strikingly in their anion selectivity. Net chloride permeability was only four times as high as net sulfate permeability, whereas chloride exchange is over 10,000 times faster than sulfate exchange. Net OH-permeability, determined by an analogous method, was over four orders of magnitude larger than that of Cl-, but was also sensitive to DIDS. These data and others are discussed in terms of the possibility that a common element may be involved in both net and exchange anion transport.

Bicarbonates↗
PubMed1978

Isolation of organic anions by extraction with liquid anion exchangers and its application to micromethods for acetylcholinesterase and 4-aminobutyrate aminotransferase.

Organic anions of particular importance to biochemistry such as Krebs cycle intermediates, glycolysis intermediates, simple fatty acids, adenine nucleotides and CoA derivatives can be quantitatively extracted from a buffered solution by high-molecular-weight ammonium salts in an organic solvent. Phosphate salts of tertiary amines in chloroform were the most efficient extractants. The isolation procedure was found to be an example of amine neutralization. The effect of pH, different inorganic anions, volume ratios between the two phases, concentration of the isolated anions and concentration of the ammonium salts have been investigated. The extraction technique has been applied to rapid and sensitive radiochemical methods for the determination of acetylcholinesterase and 4-aminobutyrate aminotransferase activities.

4-Aminobutyrate Transaminase↗
PubMed1978

Oxalate and spin-labeled oxalate as probes of the anion binding site of human transferrin. Metal to anion distance.

The spin-labeled anion N-[4-(2,2,6,6-tetramethylpiperidin-1-oxyl)] oxamate has been synthesized and characterized. In the presence of this compound, a specific iron-transferrin-anion complex is formed, as evidenced by the development of a characteristic red color. No EPR signal was observed for the nitroxyl radical in the protein complex, presumably due to broadening of the signal by the paramagnetic metal ion. Failure to observe a signal implies that the metal to nitroxyl distance is less than or equal to 6 A. This suggests that the anion is directly attached to the metal ion in the protein. The pH dependence of iron dissociation from iron-transferrin-oxalate is also reported. This complex is more stable at low pH than iron-transferrin-carbonate.

Binding Sites↗
PubMed1979

Asymmetry in the mechanism for anion exchange in human red blood cell membranes. Evidence for reciprocating sites that react with one transported anion at a time.

The kinetics of chloride and bromide transport were examined in intact human red blood cells and resealed ghosts. Because the influx and efflux of halide ions are almost equal (less than 0.01% difference), the stimulation of the exchange flux by external halides could be determined by measuring 36Cl or 82Br efflux. When the external halide concentration was increased by replacement of isoionic, isotonic solutions of sucrose and the nontransported anion citrate, the stimulation of the exchange flux was hyperbolic and was maximum at 20 mM halide externally. The K 1/2-out, the external concentration of chloride or bromide which stimulated the efflux to half of its maximum value, was 3 and 1 mM respectively, 15-fold smaller than K 1/2-in which we found to be about equal to the K 1/2 of halide self-exchange with nearly equal internal and external concentrations. Thus, the transport mechanism behaves asymmetrically with respect to these transported halides. Bromide flux was two-fold greater in bromide-chloride heteroexchange than in bromide-bromide self-exchange but it was still much smaller than the chloride self-exchange flux. The maximum influx and efflux of bromide in exchange for chloride were roughly eqal. Thus, since the maximum transport rates in the two directions are nearly equal, the kinetics of bromide equilibrium exchange with equal concentrations on the two sides are controlled on the inside where K 1/2 is greatest. The K 1/2-out Cl was a hyperbolic function of internal chloride concentration and was proportional to the maximum flux at each internal chloride concentration. These results are evaluated in terms of two broad categories of models. We conclude that, in contrast to other ion transport systems which have been shown to have kinetics of a sequential mechanism, anion exchange is compatible with a ping-pong mechanism in which a single site reciprocates between inside- and outside-facing orientations with asymmetric K 1/2 values.

Adult↗
PubMed1979

Anion transport in red blood cells. I. Chemical properties of anion recognition sites as revealed by structure-activity relationships of aromatic sulfonic acids.

The present study is concerned with the chemical factors that determine the inhibitory properties of reversible aromatic sulfonic acids on sulfate exchange system of human red blood cells. Two series of compounds were tested for inhibitory potencies: benzene sulfonic acid (BS) and 2,2'-disulfonic stilbene (DS) derivatives, each series with substituent groups such as Cl, OH, NH2, NO2, NNN, N-acetamido, and N-benzoamido. As judged by various kinetic criteria, all congeners of BS and DS appear to have common sites of action in the anion transport system. The range of inhibitory potencies, as defined by the concentration required to produce 50% inhibition (ID50), varied over a 10(4) range (ID50:2-50,000 microM). The degree of inhibition was correlated with two physicochemical properties of the substituent groups: (a) lipophilicity, as judged by the pi values (Hansch factor) of the groups; and (b) the electronic character, as judged by sigma values (Hammett factor) of the groups. Optimal correlations were obtained with a linear combination of the two factors. Based on the above structure-activity relationships and on a comparison between the inhibitory properties of congeners of BS and DS, we suggest that the microenvironment of substrate recognition sites bears a positive multipolar character and possesses functionally essential groups with electron donor capacity embedded in a hydrophobic area.

Anions↗
PubMed1975

Anion binding properties of human serum albumin from halide ion quadrupole relaxation.

The nuclear magnetic quadrupole relaxation enhancement of 35Cl-, 81Br-, and 12I- anions on binding to human serum albumin has been studied under conditions of variable protein and anion concentration and also in the presence of simple inorganic, amphiphilic, and complex anions which compete with the halide ions for the protein anion binding sites. Two classes of anion binding sites with greatly different binding constans were identified. Experiments at variable halide ion concentration were employed to determin the Cl- and I- binding constants. By means of 35 Cl nuclear magnetic resonance (NMR) the relative affinity for different anions was determined by competition experiments for both the strong and the weak anion binding sites. Anion binding follows the sequence SO42- smaller than F- smaller than CH3COO- smaller than Ci- smaller Br- smaller than NO3- smaller than I- smaller than ClO4- smaller than SCN- smaller than Pt(CN)42- smaller than Au(CN)2- smaller than CH3(CH2)11OSO3- for the high affinity sites, and the sequence SO42- congruent to F- congruent to Cl- smaller CH3COO- smaller than NO3- smaller than Br- smaller than I- smaller than ClO4- smaller than SCN- for the low affinity sites. These series are nearly identical with the well-known lyotropic series. Consequently, those effects of anions on proteins described by the lyotropic series can be correlated with the affinities of the anions for binding to the protein. The data suggest that the physical nature of the interaction is the same for both types of biding sites, and that the differences in affinity between different binding sites must be explained in terms of tertiary structure. Analogous experiments performed using 127I- quadrupole relaxation gave results very similar to those obtained with 35Cl-. A comparison between the Cl-, Br- and I- ions revealed that, as a result of the increasing affinity for the weak anion binding sites in the series Cl- smaller than Br- smaller than I-, Cl- is much more useful as a probe for the specific anion binding sites than the other two halide ions. The findings with human serum albumin in this and other respects are probably of general relevance in studies of protein-anion interactions. In addition to competition experiments, the magnitude of the relaxation rate is also discussed. Line broadening not related to anion binding to the protein is found to be small. A comparison of transverse and longitudinal 35Cl relaxation rates gives a value for the quadrupole coupling constant of the high affinity sites in good agreement with a calculated coupling constant assuming anion binding to arginine.

Anions↗
PubMed1979

The linkage between the four-step binding of oxygen and the binding of heterotropic anionic ligands in hemoglobin.

The linkage between the four-step binding of oxygen and the binding of heterotropic anionic ligands in hemoglobin was investigated by accurately measuring and analyzing the oxygen equilibrium curves of human adult hemoglobin in the presence and absence of various concentrations of one or two of the following materials: chloride (Cl-), 2,3-diphosphoglycerate (DPG), and inositol hexaphosphate (IHP). Each equilibrium curve was analyzed according to the Adair equation to evaluate the four-step oxygen equilibrium constants (Adair constants) and the median oxygen pressure. The binding constants of the anions for the molecular species of hemoglobin carrying j oxygen molecules, Hb(O2)j(j=0,1,...,4), were evaluated from the dependences of the Adair constants and the median oxygen pressure on the anion concentration by introducing a model which takes the competitive binding of Cl- and DPG or IHP into account. Assumptions made in the model are: (a) the hemoglobin molecule has two oxygen-linked binding sites for Cl- which are equivalent and independent and (b) no Cl- can be bound to hemoglobin to which DPG or IHP is already bound and vice versa. Thus, we could obtain values for the intrinsic binding constants of Cl- and DPG, i.e., the constants in the absence of other competitive anions. For IHP, only the binding constants and apparent binding constants for Hb and Hb(O2)2 were obtained. Values of the Cl- binding constants and apparent binding constants for DPG and IHP, i.e., the binding constants in the presence of Cl- for Hb and Hb(O2)4, were in reasonable agreement with literature values. From the binding constants we calculated anion binding curves for Hb(O2)j(J=0,1,...,4), the number of anions bound to Hb(O2)J, And the relationship between fractional anion saturation of hemoglobin and fractional oxygen saturation. The numbers of released anions are not uniform with respect to oxygenation step. This non-uniformity is the reason for the changes in the shape of the oxygen equilibrium curve with anion concentration changes and for the non-uniform dependences of the Adair constants on anion concentration, and also results in non-linear relations between anion saturation and oxygen saturation. The anion binding constants and various binding properties of the anions derived from those constants are consistent with those observed by other investigators using different techniques, indicating that the present model describes the oxygen-linked competitive anion binding well.

Adult↗
PubMed1977

Anion selectivity in biological systems.

As background for appreciating the still-unsolved problems of monovalent anion selectivity, we summarize the facts and intepretations that seem reasonably well established. In section II we saw that specific effects of monovalent anions on biological and physical systems define qualitative patterns, in that only certain sequences of anion effects are observed. For example, the 4 halides can be permitted on paper as 4! = 24 sequences, yet only 5 of these sequences have been observed in nature as potency sequences. In addition, there are quantitative regularities in anion potency that permit the construction of so-called empirical selectivity isotherms (Figs. 4 and 13). That is, a given potency sequence is found to be associated with only a certain modest range of selectivity ratios. The sequences and isotherms apply to effects with a nonequilibrium component (e.g., permeability and conductance sequences) as well as to purely equilibrium effects. Since students of cation selectivity have had difficulty accepting this conclusion, we discuss the reasons why it is not as paradoxical as it at first seems. In sections III and IV we develop four theoretical models to account for the observed anion potency sequences as sequences of equilibrium binding energies. Two of these models involve calculation of electrostatic binding energies between anions and monopolar or dipolar cationic sites, assuming anions as well as sites to be rigid and nonpolarizable. The other two models use thermochemically measured binding energies between anions and thealkali cations or occasionally alkaline-earth cations, which in fact approximate rigid, nonpolarizable spheres. All four models consider the anion selectivity pattern of a given cationic site to be determined by anion differences in the balance between hydration energies and ion-site binding energies. Site differences in anion selectivity pattern are attributed to site differences in radius, charge, coordination number, or dipole length. These models succeed in predicting all five observed selectivity sequences of the halides. The models predict in addition the possible existence of two further halide sequences that arise from very strong sites and that have not yet been observed in nature. For polyatomic anions the predictions agree approximately but not completely with observations. Thyroidlike systems, which greatly prefer iodide over other halides,re interpreted as having the weakest sites. Site hydration is predicted to affect the magnitude but not the sequence of potency ratios. For the thyroidlike systems, observed potency ratios are smaller than would be expected if anions were completely dehydrated at biological sites.

Animals↗
PubMed1979

pH and bicarbonate effects on mitochondrial anion accumulation. Proposed mechanism for changes in renal metabolite levels in acute acid-base disturbances.

Mitochondria from rabbit and dog renal cortex were incubated with 1 mM (14)C-weak acid anions in media containing low (10 mM) or high (40 mM) concentrations of bicarbonate and the steady-state accumulation of labeled anion in the matrix was measured. In the absence of an energy source, no concentration of (14)C-anion in the mitochondrial matrix space was present, but the anion concentration was significantly higher at low- than at high-bicarbonate concentration. Addition of an energy source, usually ascorbate plus tetramethyl-p-phenylenediamine, led to increases in matrix space anion levels and to accentuation of the difference in anion uptake between low- and high-bicarbonate media, so that two to four times as much anion was present at low- than at high-bicarbonate concentrations. The anions affected included substrates for which inner membrane carriers are present in mitochondria, such as citrate, alpha-ketoglutarate, malate, and glutamate, as well as substances which diffuse passively across the inner membrane such as acetate and formate. When a nonbicarbonate medium buffered with Hepes was used, pH change did not alter anion uptake although anion concentrations exceeding those in the medium still developed when an energy source was present. The difference in mitochondrial anion accumulation between low- and high-bicarbonate levels diminished with decreasing temperature or with increasing anion concentration in the medium. Estimation of intramitochondrial pH with [(14)C]5,5-dimethyl-oxazolidine-2,4-dione showed that the pH gradient across the inner mitochondrial membrane was significantly greater with 10 than with 40 mM bicarbonate in the medium.A hypothesis is described that relates this effect of pH and bicarbonate on mitochondrial anion accumulation to the very rapid changes in substrate levels in renal cortex, which develop when acute metabolic acidosis or alkalosis is produced in the intact animal. It is suggested that an abrupt fall in systemic pH and bicarbonate is associated with a shift in substrate in renal cortex out of the cytoplasm and into mitochondria, where some of the added substrate is metabolized. Reduction in the size of the cytoplasmic pool of substrate occurs with relatively little accompanying change in the size of the mitochondrial pool, thus causing a net reduction in the total tissue pool. This mechanism accounts for the reduction in tissue levels of many mitochondrial substrates observed acutely in metabolic acidosis. In metabolic alkalosis, reversal of these effects leads to expansion of the cytoplasmic pool, thereby resulting in the rise in tissue levels of substrates which occurs in this condition.

Acid-Base Imbalance↗
PubMed1978

Anion binding to yeast phosphoglycerate kinase.

The single thiol of yeast phosphoglycerate kinase was labelled with the chromophoric sulfhydryl reagent, 2-chloromercuri-4-nitrophenol. Sequential additions of individual anions to this modified enzyme brought about a decrease in absorbance at 410 nm that reflected the degree of saturation of the enzyme with anion. The binding curves were analyzed to determine the dissociation constants of a number of anions with charges varying from--1 to--4.1. A linear relationship was found between the charge of the anion and the negative logarithm of the dissociation constant for the labelled enzyme-anion complex. The highly charged anions, such as ATP, bound more tightly than did anions with less charge, such as Cl-. The average number of binding sites for those anions for which accurate results could be obtained was 1.06 mol per 47000 g of enzyme. Several lines of evidence suggested that titration of the active center was not being monitored. Anions bound to phosphoglycerate kinase decreased the rate of reaction between the enzyme thiol and 5,5'-dithiobis(2-nitrobenzoic acid). The relationship between the degree of saturation of the anion binding site and the reaction rate constant was used to calculate the dissociation constant between anion and enzyme. Dissociation constants determined in this manner were in good agreement with those determined by titration of the enzyme-mercurial complex.

Anions↗
PubMed1975

The distribution of anionic sites on the surfaces of mitochondrial membranes. Visual probing with polycationic ferritin.

Polycationic ferritin, a multivalent ligand, was used as a visual probe to determine the distribution and density of anionic sites on the surfaces of rat liver mitochondrial membranes. Both the distribution of bound polycationic ferritin and the topography of the outer surface of the inner mitochondrial membrane were studied in depth by utilizing thin sections and critical-point dried, whole mount preparations for transmission electron microscopy and by scanning electron microscopy. Based on its relative affinity for polycationic ferritin, the surface of the inner membrane contains discrete regions of high density and low density anionic sites. Whereas the surface of the cristal membrane contains a low density of anionic sites, the surface of the inner boundary membrane contains patches of high density anionic sites. The high density anionic sites on the inner boundary membrane were found to persist as stable patches and did not dissociate or randomize freely when the membrane was converted osmotically to a spherical configuration. The observations suggest that the inner mitochondrial membrane is composed of two major regions of anionic macromolecular distinction. It is well-known that an intermembrane space exists between the two membranes of the intact mitochondrion; however, a number of contact sites occur between the two membranes. We determined that the outer membrane, partially disrupted by treatment with digitonin, remains attached to the inner membrane at these contact sites as inverted vesicles. Such attached vesicles show that the inner surface of the outer membrane contains anionic sites, but of decreased density, surrounding the contact sites. Thus, the intermembrane space in the intact mitochondrion may be maintained by electronegative surfaces of the two mitochondrial membranes. The distribution of anionic sites on the outer surface of the outer membrane is random. The nature and function of fixed anionic surface charges and membrane contact sites are discussed with regard to recent reports relating to calcium transport, protein assembly into mitochondrial membranes, and membrane fluidity.

Animals↗
PubMed1976

Anion and amine uptake and uncoupling in submitochondrial particles.

1. Unlike chloroplasts, submitochondrial particles are not uncoupled by nigericin + KCl or NH4Cl. Also the uncoupling effect of lipophilic anions is largely independent of the addition of weak bases. 2. Low concentrations of permeant anions cause a shift of the steady-state energy level rather than a cycle of energy utilization. The degree of inhibition of ATP synthesis by tetraphenylboron is larger than required for the uptake of the anion. 3. Lipophilic anions such as bromthymolblue, bromcresolpurple, and 8-anilino-1-napthalene sulphonate cause a pH-independent, 50% uncoupling in submitochondrial particles at concentrations of 3, 30 and 30 muM, respectively. The passive interaction of bromthymolblue and bromcresolpurple appears as a pH-dependent distribution between two pHases. ATP causes a pH-independent slight shift in the anion distribution, with negligible anion accumulation. 4. Addition of amines to energized submitochondrial particles results in two types of effects; uptake of amines and uncoupling. While in chloroplasts amine uptake and uncoupling are closely associated, this is not the case in submitochondrial particles. The uncoupling effect is observed only with lipophilic and not with hydrophilic amines, and the degree of uncoupling increases with the lipophilicity of the amines. The amine uptake, on the other hand, is accompanied by negligible uncoupling. 5. While the uptake of amines is dependent on the presence of non-permeant anions, such as Cl-, the uncoupling effect is independent of Cl-. Furthermore the amine uncoupling is markedly enhanced by lipophilic anions. 6. The view is discussed that the uncoupling effect of lipophilic anions and lipophilic amines in submitochondrial particles is due to a catalytic energy dissipation rather than to a stoichiometry energy utilization. The molecular mechanism of uncoupling presumably involves a cycling of charges after a perturbation of the membrane structure.

Amines↗
PubMed1978

Reversible inhibition of anion exchange in human erythrocytes by an inorganic disulfonate, tetrathionate.

Tetrathionate (S4O6--) markedly inhibits anion exchange across the human erythrocyte membrane. This phenomenon has been studied in order to obtain further insight into the mechanism of action of reversible inhibitors, in particular disulfonate inhibitors, of anion exchange. Anion fluxes were measured by tracer techniques at equilibrium. The following results were obtained: Tetrathionate, although an inorganic compound, inhibits the self-exchange of sulfate and of divalent organic anions (oxalate, malonate) noncompetitively at Ki values (less than or equal to 0.5 mM) as yet only observed for amphiphilic inhibitors. The inhibitor is effective only from the outside of the cell. The inhibition is temperature-dependent, Ki increasing by a factor of 5 between 5 and 35 degrees C, and instantaneously and fully reversible. The presence of small monovalent anions (fluoride, bromide, chloride, nitrate, acetate) counteracts inhibition by tetrathionate to a varying and concentration-dependent extent, divalent anions have only a minor effect at high concentrations. Chloride exchange is also inhibited, while glycolate and lactate fluxes are much less sensitive or almost insensitive, in agreement with their alleged transfer by a different transport system. Tetrathionate is unique in its inhibitory action, its structural congeners, peroxodisulfate (S2O8--) and ethanedisulfonate (C2H4S2O6--) are much less effective. The results can be interpreted by assuming that tetrathionate inhibits the movement of anions via the inorganic anion exchange system by binding--in a 1 : 1 stoichiometry--to inhibitory "modifier sites", for which it competes with other anions. These sites are located only on the exofacial surface of the membrane. The high affinity of tetrathionate is probably due to a local excess of pi electrons in the region of its central disulfide bond. These may stabilize the binding by their ability to form electron donor-acceptor complexes with membrane sites, thus compensating for the absence of a hydrophobic binding domain in tetrathionate.

Binding Sites↗