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A K Solomon

Publications and source records attributed to A K Solomon.

At least 55 records · Page 3Linked to original sources
PubMed1982

Interaction of phloretin with the anion transport protein of the red blood cell membrane.

Phloretin is an inhibitor of anion exchange and glucose and urea transport in human red cells. Equilibrium binding the kinetic studies indicate that phloretin binds to band 3, a major integral protein of the red cell membrane. Equilibrium phloretin binding has been found to be competitive with the binding of the anion transport inhibitor, 4,4'-dibenzamido-2,2'-disulfonic stilbene (DBDS), which binds specifically to band 3. The apparent binding (dissociation) constant of phloretin to red cell ghost band 3 in 28.5 mM citrate buffer, pH 7.4, 25 degree C, determined from equilibrium binding competition, is 1.8 +/- 0.1 microM. Stopped-flow kinetic studies show that phloretin decreases the rate of DBDS binding to band 3 in a purely competitive manner, with an apparent phloretin constant of 1.6 +/- 0.4 microM. The pH dependence of equilibrium binding studies show that it is the charged, anionic form of phloretin that competes with DBDS binding, with an apparent phloretin inhibition constant of 1.4 microM. The phloretin binding and inhibition constants determined by equilibrium binding, kinetic and pH studies are all similar to the inhibition constant of phloretin for anion exchange. These studies suggest that phloretin inhibits anion exchange in red cells by a specific interaction between phloretin and band 3.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1982

A stepwise mechanism for the permeation of phloretin through a lipid bilayer.

The thermodynamics of interactions between phloretin and a phosphatidylcholine (PC) vesicle membrane are characterized using equilibrium spectrophotometric titration, stopped-flow, and temperature-jump techniques. Binding of phloretin to a PC vesicle membrane is diffusion limited, with an association rate constant greater than 10(8) M-1s-1, and an interfacial activation free energy of less than 2 kcal/mol. Equilibrium binding of phloretin to a vesicle membrane is characterized by a single class of high-affinity (8 micro M), noninteracting sites. Binding is enthalpy driven (delta H = -4.9 kcal/mol) at 23 degrees C. Analysis of amplitudes of kinetic processes shows that 66 +/- 3% of total phloretin binding sites are exposed at the external vesicle surface. The rate of phloretin movement between binding sites located near the external and internal interfaces is proportional to the concentration of un-ionized phloretin, with a rate constant of 5.7 X 10(4) M-1s-1 at 23 degrees C. The rate of this process is limited by a large enthalpic (9 kcal/mol) and entropic (-31 entropy units) barrier. An analysis of the concentration dependence of the rate of transmembrane movement suggests the presence of multiple intramembrane potential barriers. Permeation of phloretin through a lipid bilayer is modeled quantitatively in terms of discrete steps: binding to a membrane surface, translocation across a series of intramembrane barriers, and dissociation from the opposite membrane surface. The permeability coefficient for phloretin is calculated as 1.9 X 10(-3) cm/s on the basis of the model presented. Structure-function relationships are examined for a number of phloretin analogues.

Flavanones↗
PubMed1981

Relation between red cell membrane (Na+ + K+)-ATPase and band 3 protein.

This study is designed to examine the participation of the major red cell membrane protein, band 3 protein, in the chain which transmits information from the cardiac glycoside site on the external face of the cell (Na+ + K+)-ATPase to the megadalton glycolytic enzyme complex within the cell. The experiments show that the anion transport inhibitor, 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid, affects the resonance of 2,3-diphosphoglycerate, as does the cardiac glycoside cation transport inhibitor, ouabain. Resonance shifts induced by the cardiac glycoside alone are modulated by addition of the anion transport inhibitor which indicates that there is coupling in the red cell between the (Na+ + K+)-ATPase and band 3 protein. Band 3 protein was separated from the membrane and partially purified following the technique of Yu and Steck ((1975) J. Biol. Chem. 250, 9170-9175). When glyceraldehyde-3-phosphate dehydrogenase was added to the separated band 3 protein preparation, addition of cardiac glycosides caused shifts in the 31P resonance of glyceraldehyde 3-phosphate. These experiments indicate that there is coupling between the (Na+ + K+)-ATPase and band 3 protein in the separated preparation and suggest that the anion and cation transport systems may be closely related spatially and functionally in the intact red cell.

2,3-Diphosphoglycerate↗
PubMed1981

Osmotic water permeability of human red cells.

The osmotic water permeability of human red cells has been reexamined with a stopped-flow device and a new perturbation technique. Small osmotic gradients are used to minimize the systematic error caused by nonlinearities in the relationship between cell volume and light scattering. Corrections are then made for residual systematic error. Our results show that the hydraulic conductivity, Lp, is essentially independent of the direction of water flow and of osmolality in the range 184-365 mosM. the mean value of Lp obtained obtained was 1.8 +/- 0.1 (SEM) X 10-11 cm3 dyne -1 s-1.

Cell Membrane Permeability↗
PubMed1980

Improved stop-flow apparatus to measure permeability of human red cells and ghosts.

An improved stop-flow apparatus has been designed and constructed to measure the permeability characteristics of human red cells, which can be inferred from the time course of red cell volume changes following a sudden change in cellular environment produced by a raped mixing device. The improved apparatus is directly coupled to a computer which automates the subtraction and averaging procedures that have been developed to minimize the noise generated in the system by the cessation of red cell forward motion when the flow is suddenly stopped. Real time data acquisition also makes it possible to increase the number of data points by an order of magnitude, thus improving accuracy significantly. The apparatus has been tested by measurements of the human red cell hydraulic permeability coefficient. Data are presented to validate the subtraction procedure. Experiments have also been carried out on red cell ghosts which indicate that the hydraulic conductivity of the ghost is similar to that of the undisturbed red cell.

Adult↗
PubMed1980

Kinetics of phloretin binding to phosphatidylcholine vesicle membranes.

The submillisecond kinetics for phloretin binding to unilamellar phosphatidylcholine (PC) vesicles was investigated using the temperature-jump technique. Spectrophotometric studies of the equilibrium binding performed at 328 nm demonstrated that phloretin binds to a single set of independent, equivalent sites on the vesicle with a dissociation constant of 8.0 microM and a lipid/site ratio of 4.0. The temperature of the phloretin-vesicle solution was jumped by 4 degrees C within 4 microseconds producing a monoexponential, concentration-dependent relaxation process with time constants in the 30--200-microseconds time range. An analysis of the concentration dependence of relaxation time constants at pH 7.30 and 24 degrees C yielded a binding rate constant of 2.7 X 10(8) M-1 s-1 and an unbinding constant of 2,900 s-1; approximately 66 percent of total binding sites are exposed at the outer vesicle surface. The value of the binding rate constant and three additional observations suggest that the binding kinetics are diffusion limited. The phloretin analogue, naringenin, which has a diffusion coefficient similar to phloretin yet a dissociation constant equal to 24 microM, bound to PC vesicle with the same rate constant as phloretin did. In addition, the phloretin-PC system was studied in buffers made one to six times more viscous than water by addition of sucrose or glycerol to the differ. The equilibrium affinity for phloretin binding to PC vesicles is independent of viscosity, yet the binding rate constant decreases with the expected dependence (kappa binding alpha 1/viscosity) for diffusion-limited processes. Thus, the binding rate constant is not altered by differences in binding affinity, yet depends upon the diffusion coefficient in buffer. Finally, studies of the pH dependence of the binding rate constant showed a dependence (kappa binding alpha [1 + 10pH-pK]) consistent with the diffusion-limited binding of a weak acid.

Hydrogen-Ion Concentration↗
PubMed1979

Calcium-induced potassium pathway in sided erythrocyte membrane vesicles.

We have characterized the asymmetric effect of Ca2+ on passive K+ permeability in erythrocyte membranes, using inside out and right-side out vesicles. Ca2+, but not Mg2+, can induce an increase in K+ uptake in inside out vesicles. The half-maximal concentration of Ca2+ required to induce the K+ uptake is 0.2 mM, and the permeability increase is not specific for K+. Thus, the Ca2+- induced permeation process in inside out vesicles is changed from that in the energy-depleted intact cell which requires only micromolar concentrations of Ca2+ and is specific for K+. Removal of spectrin had no effect on the vesicle permeability increase due to Ca2+. Studies with N-ethylmaleimide show that the vesicle channel openings is mediated by a protein and passage is controlled by sulfhydryl groups; furthermore, the Ca2+-induced vesicle pathway is distinct from the normal channel for passive K+ leak in the absence of Ca2+. The protein is sensitive to its phospholipid environment since removal of easily accessible phospholipid head groups on the cytoplasmic face of the vesicles inhibits the Ca2+ -stimulated channel opening.

Biological Transport↗
PubMed1979

Effect of the sodium/potassium ratio on glyceraldehyde 3-phosphate dehydrogenase interaction with red cell vesicles.

Binding of glyceraldehyde 3-phosphate to glyceraldehyde-3-phosphate dehydrogenase, the membrane protein known as Band 6, causes shifts in the 31P nuclear magnetic resonance spectrum of the substrate (Fossel, E.T. and Solomon, A.K (1977) Biochim. Biophys. Acta 464, 82--92). We have studied the resonance shifts produced by varying the sodium/potassium ratio, at constant ionic strength, in order to examine the relationship between the cation transport system and glyceraldehyde-3-phosphate dehydrogenase. Alteration of the potassium concentration at the extracellular face of the vesicle affects the conformation of glyceraldehyde-3-phosphate dehydrogenase at the cytoplasmic face, thus showing that a conformation changed induced by a change in extracellular potassium can be transmitted across the membrane. Alterations of the sodium concentration at the cytoplasmic face also affect the enzyme conformation, whereas sodium changes at the extracellular face are without effect. In contrast, there is no sidedness difference in the effect of potassium concentrations. The half-values for these effects are like those for activation of the red cell (Na4 + K+)-ATPase. We have also produced ionic concentration gradients across the vesicle similar to those Glynn and Lew (1970) J. Physiol. London 207, 393--402) found to be effective in running the cation pump backwards to produce adenosine triphosphate in the human red cell. The sodium/potassium concentration dependence of this process in red cells is mimicked by 31P resonance shifts in the (glyceraldehyde 3-phosphate/glyceraldehyde-3-phosphate dehydrogenase/inside out vesicle) system. These experiments provide strong support for the existence of a functional linkage between the membrane (Na+ + K+)-ATPase and the glyceraldehyde-3-phosphate dehydrogenase at the cytoplasmic face.

Adenosine Triphosphate↗
PubMed1979

Permeability of human erythrocyte membrane vesicles to alkali cations.

The permeability of inside-out and right-side-out vesicles from erythrocyte membranes to inorganic cations was determined quantitatively. Using 86Rb as a K analog, we have measured the rate constant of 86Rb efflux from vesicles under equilibrium exchange conditions, using a dialysis procedure. The permeability coefficients of the vesicles to Rb are only about an order of magnitude greater than that of whole erythrocytes. Furthermore, we have measured many of the specialized transport systems known to exist in erythrocytes and have shown that glucose, sulfate, ATP-dependent Ca and ATP-dependent Na transport activities are retained by the vesicle membranes. These results suggest that inside-out and right-side-out vesicles can be used effectively to study transport properties of erythrocyte membranes.

Adenosine Triphosphate↗
PubMed1978

Ouabain-sensitive interaction between human red cell membrane and glycolytic enzyme complex in cytosol.

Binding of 2,3-diphosphoglycerate to monophosphoglycerate mutase, of which it is an obligatory cofactor, causes changes in the resonance positions of the 31P nuclear magnetic resonance spectra of both phosphate groups. It has previously been shown that these resonances shift when other glycolytic enzymes, such as phosphoglycerate kinase, are added to form the 2,3-diphosphoglycerate . monophosphoglycerate mutase . phosphoglycerate kinase complex. In view of this association, we have examined the set of glycolytic enzymes from aldolase to pyruvate kinase and found evidence of direct communication between all of these enzymes. A multi-enzyme complex of 1--2 . 10(6) daltons has been separated from broken cell ghosts by Biogel column filtration and evidence has been presented to show that this complex exhibits aldolase, glyceraldehyde 3-phosphate dehydrogenase and phosphoglycerate kinase activity. The glycolytic multi-enzyme complex interacts with the outer face of inside-out vesicles prepared from human red cells and the interaction is suppressed by application of 10(-6) M ouabain to the inner face of these vesicles. These studies show that the conformation of the enzymes comprising the megadalton complex are responsive to the application of ouabain to the outer red cell membrane surface.

Cytosol↗
PubMed1977

Membrane permeability equations and their solutions for red cells.

The mathematical equations for the transport of nonelectrolytes across cell membranes are critically examined and cast in forms suitable for solution which involve fewer approximations than has heretofore been commonly done. For the use of red cells, the equations are developed to include the effect of the variation in apparent nonosmotic water owing to the variation in hemoglobin concentration as the cell swells or shrinks. Two methods of solution of the equations are developed and studied and sample calculations are provided. It is shown that the solutions to the linearized equations commonly found in the literature are insufficiently accurate for some purposes and this inaccuracy is avoided by the methods given here. The importance of retaining the effects of variations in apparent nonosmotic water and in solute volume in the cell is demonstrated.

Cell Membrane Permeability↗
PubMed1977

Membrane mediated link between ion transport and metabolism in human red cells.

When 10(-6) M oubain is added to human red cell that have been incubated without glucose for two hours, there is a significant shift in the 31P nuclear magnetic resonances of both phosphate groups of cellular 2,3-diphosphoglycerate, which is not found in control cells incubated with glucose. This means that an effect induced by ouabain on the outside of the red cell membrane is transmitted through the membrane to alter the environment of an intracellular metabolite. Experiments with glycolytic cycle inhibitors have indicated that the intracellular ligand responsible for the resonance shifts is monophosphoglycerate mutase which requires 2,3-diphosphoglycerate as a cofactor for the reaction it catalyzes. To account for this finding a hypothesis is presented that the (Na+ + K+)-ATPase in human red cells is linked to monophosphoglycerate mutase through the agency of phosphoglycerate kinase. Evidence is presented for the existence of phosphoglycerate kinase/monophosphoglycerate mutase in solution. It is shown that this complex can interact with the cytoplasmic face of (Na+ + K+)-ATPase at the outside surface of inside out red cell vesicles, and that this interaction is inhibited when 10(-6) M ouabain is contained within the vesicle. Neither monophosphoglycerate mutase nor phosphoglycerate kinase is significantly bound to the inside surface of the intact human red cell, but glyceraldehyde 3-phosphate dehydrogenase is; it is shown that this enzyme also interacts with the cytoplasmic face of the (Na+ + K+)-ATPase and that the interaction is inhibited by 10(-6) M ouabain.

Biological Transport, Active↗
PubMed1976

Modulation of 2,3-diphosphoglycerate 31P-NMR resonance positions by red cell membrane shape.

Na+ transport in the red cells of the dog is dependent on cell volume, a 20% change in cell volume leading to a 25-fold increase in apparent Na+ flux; the effect is dependent upon metabolic energy. We have found that swelling and shrinking dog red cells causes a shift in the 31P-NMR peak of 2,3-diphosphoglycerate, which is present in dog red cells at 5.5 mM. Control experiments indicate that the 2,3-diphosphoglycerate resonance peak shifts may not be attributed to: interaction with hemoglobin, changes in cell pH, ionic strength, diamagnetic susceptibility or small changes in the Mg2+/2,3-diphosphoglycerate ratio. Experiments with chlorpromazine and pentanol which alter red cell membrane area by a mechanism different from osmotic swelling suggest that 2,3-diphosphoglycerate interacts with a binding site in the cell that is dependent upon the physical condition of the dog red cell membrane.

Animals↗
PubMed1976

Nonelectrolyte diffusion across lipid bilayer systems.

The permeability coefficients of a homologous series of amides from formamide through valeramide have been measured in spherical bilayers prepared by the method described by Jung. They do not depend directly on the water:ether partition coefficient which increases regularly with chain length. Instead there is a minimum at acetamide. This has been ascribed to the effect of steric hindrance on diffusion within the bilayer which increases with solute molar volume. This factor is of the same magnitude, though opposite in sign to the effect of lipid solubility, thus accounting for the minimum. The resistance to passage across the interface has been compared to the resistance to diffusion within the membrane. As the solute chain length increases the interface becomes more important, until for valeramide it comprises about 90% of the total resistance. Interface resistance is also important in urea permeation, causing urea to permeate much more slowly than an amide of comparable size, after allowance is made for the difference in the water:ether partition coefficient. Amide permeation coefficients have been compared with relative liposome permeation data measured by the rate of liposome swelling. The ratios of the two measures of permeation vary between 3 and 16 for the homologous amides. The apparent enthalpy of liposome permeation has been measured and found to be in the neighborhood of 12 kcal mol-1 essentially independent of chain length. Comparison of the bilayer permeability coefficients with those of red cells shows that red cell permeation by the lipophilic solutes resembles that of the bilayers, whereas permeation by the hydrophilic solutes differs significantly.

Amides↗